I'd like to introduce Christian Hilchi from the University of Texas at Austin, and he's going to be talking to us today about his project reality check or embracing open the reality check project. Christian it's all yours. All right, thank you Carl. Um, so yeah so I'm going to be talking about my project reality check this is a project that started in 2014. It was sponsored by the Center for European Studies as well as my home department the Department of Slavic and Eurasian studies, and I worked intimately with Carl and Natalie here with the Center for open educational resources and language learning. A phenomenal aid in terms of the advice as well as the tech support, graphical design all sorts of issues that that I needed help with so I'm really grateful for everything that they did and continue to do reality check is under a CC by essay license I chose this license. Not only because of the my overall agreement with the license and I really like what it what it enables in terms of sharing and sort of creating, you know, promoting the ethos the open ethos that is going to mean that you know if I create this resource. If other people want to work on it they're going to contribute back to to altering my project. In the end, it also was because I was finding that was using a lot of share like content from with media comments as well as other sites. I really wanted to use that and it was really integrated very tightly into the into the project so it was kind of a necessity to choose that license. But overall I think it was a choice that I would would happily make again. It ended up being quite a massive project much bigger than I ever expected. I mean here you can see just some of the figures that are associated with it. So, you know, we lots of grammar and culture lessons quizzes that are located on canvas and activity book as well as homework exercises that are printable interview videos that I'll talk about in a minute map videos as well as lots of use of Quizlet for the platform. Now, why reality check and actually before I even talked about that I want to talk about this graphic here. This is one of Natalie's creations and it's meant to look like a beer coaster the checks are really well known for their, their very good beer. And so we wanted something that sort of captured that aspect of their culture. It started off with these reality style interviews that were filmed in Prague as well as in Austin we have some Czech students that come every semester to UT. And it was because I had come up with these lists of questions that every student needed to answer for various units that I was using in a previous textbook. And they actually take those those questions and film native speakers answering them. And the result was here is just one example. What do you do when you have a headache and I'll just start playing the video just so you can get an idea what these interview videos look like. So this is how they are arranged on our website. So we have them divided into novice intermediate and intermediate advanced. That's just a result of the fact that I had so many speakers who had volunteered to be in the videos that and I was finding actually that some were more you know very simple answers one two words a sentence maybe two sentences at most and some people were really responding in paragraph like utterances. And since I had that material it really made sense to utilize them and make them available to the public I will note though for the textbook itself I only utilize those from the novice intermediate because this course is geared for a or towards a beginning. Check language instruction course. So the course is run. It's a flipped classroom. There's a pre class in class. Components and post class components. And it's just a cycle that keeps repeating every day. And this is what the pre class looks like now if you want to take a look at any of these materials you can go to reality check dot org, and you will see it like this so this is how it exists on. And this is what the pre class looks like now if you want to take a look at any of these materials you can go to reality check dot org, and you will see it like this so this is how it exists on the publicly facing website, and various aspects of the course here So for example, if you were if you had access to the key you would see that some of these are grammar explanations, Quizlet is obvious there's some, some various quizzes usually auto grade type quizzes to test knowledge of the of the topics that we're learning. Pre class involves a lot of just, you know, just these various thematically related explanations, as you can see I like to use a lot of pictures in there something I'm going to talk about in just a minute. Pre class also includes canvas quizzes a lot of these are, as I said fill in the blank or multiple choice something that can be graded and they can and the students can get feedback immediately. I use a lot of Quizlet in the curriculum and I tried to use it to its utmost so basically anything that I could think of that could work within within Quizlet parameters of all the different types of activities that they have. I tried to utilize those in thoughtful ways in the course. So in their course modules when vocabulary is introduced, or even grammar topics I use Quizlet as a way to quickly reinforce those forms in class is all about practicing the language in various scenarios also using games things like that and I tried to really utilize all of the positive aspects of Google Drive. So, here you can see for example on the left. This is a memory type game you can download a set of cards so this links to another Google Doc where you can, you can click on it to get all those cards print them out cut them out and have them available for class. Similarly, oftentimes activities are given not only in the activity book but as a PowerPoint type presentation or rather Google Slides, and you can click on those and get access to those as well. So I really like to utilize a lot of reality in the textbook so here's just one example where we're talking about clothing preferences and giving opinions on clothing and, and this one YouTube user decided to give three examples of a work outfit that they like and ask the viewers you know what do you think you like the best and so this is a perfect opportunity for us to use reality, and really also show the students how much they've learned you know they walk away from these types of activities I never knew that I would have actually, you know, understood that much after that being are doing check for just a few months. So I'm going to skip this one for here. Post class is given either at the end of a canvas module or here on the public course site on the right hand side. These are various Google Docs and these Google Docs again. They involve more of the type of use of language that builds from the skills that we learned in the pre-class in the in class. So, lots of creating with language, giving opinions, or coming up with their own descriptions, things like that. Oftentimes also I take advantage of the fact that we do have access to stores, for example, so why not send them shopping so there's just one example taken from an assignment where they have to do some shopping for groceries and plan a meal at Tesco in Prague. So, getting to the title of my presentation which was embracing open. I've kind of identified three different areas where I feel that the reality check really tried to take advantage and leverage all of the open or all of the sort of the values of openness that we often talked about. And one was really reusing and remixing of other content that's currently available. In other words, not reinventing the wheel. And so, you know, we know about this in terms of talking about the five hours. So, you know, there's so much material that's out there why not take advantage of this and so this involved lots of different repositories of open images, literally thousands and thousands of images have been used throughout the, throughout the curriculum. And just as you saw from a few examples, images are a constant presence in the course, everything from clip art to to actual photos from places like Wikimedia Commons or all of the different public domain websites as well. And I use them, I try to use them in creative ways so it might be creating mean like content and using that to teach words and phrases or just to, you know, sometimes when you're when you're doing something really tough. It's kind of fun for the students to run across some sort of funny content. Or even if we're trying to learn various words and phrases or grammar so in check.  Or if you want to say my head hurts literally head hurts me or this is one of my favorite ones that I bring up a lot. Trying to learn irregular verb forms just trying to use them and fun creative ways that helps students help these these students to retain or understand better some of the the concepts that we're learning. Now I mentioned pictures but let me talk about video as well. One of the things that I found really helpful in terms of the creation of these materials was the amazing world of blogs. There are people who create content posted under an open license on YouTube on Vimeo. And they have pretty rich channels in fact when you find one of these users, you can then click on their channel and of course you find that they always publish their content or often publish their content under a creative comments license. And so really was about, you know, making that discovery and this is one of the sort of critical moments for reality check was making this discovery that all this great content out there exists. So it's under an open license, I can use it, edit it, create sort of custom versions of it for my class. And so that's something that I tried to utilize in all of the chapters. And it can be as simple as something like a drone video that I use in the first unit. So just something where we, you know, get a chance to see Prague, and while we're at it let's talk about the things we see and of course we see lots of them so that's a natural of who packs up the plural set are so really trying to to use open media to its fuller of the extent really sort of realizing all of the affordances of open that there's this stuff out there for us so let's see if we can integrate it let's really sort of, you know, buy into the whole open project. I actually identified a number of international keywords, sort of these video genres that you can use and I think these are really helpful. You know, typing in vlog, just as an English word, and then typing in all sorts of words in the target language can get tons of great content, and not only videos related to that search but also finding those channels of users who are posting lots of open content. And I've given you some other ones here such as time lapse hall unboxing and room door and these are, as I said really fruitful genres for those considering trying to integrate openly licensed video into the curriculum. Use of platforms which allow for EC export of materials and and really this comes down to using Google and Quizlet. These are also tools that I think are helpful because we all, or most of us have used these we feel comfortable with them. So, if I want to, for example, make sure that my users can, for example, redistribute revise remix they can do these to my to my materials because that's my goal really. I want my my the people who use my forms to come up with their own custom versions to show me something that I didn't know. So this project to have continuity beyond me when I will no longer have an interest in the project that this can keep going. I want to make sure that the materials are in a format that make it makes it easy for them to be edited. And so if you go to any of the content sites on on reality check or you'll see that you can open up in three different formats, Google PDF and word. And so this really helps maintain the spirit of those five hours. Additionally, I have provided canvas export so if any instructor out there wants to adopt the whole force, including all the canvas content. This canvas content is available all the quizzes for example are available to the public over the publicly facing website. But if you want quizzes that are going to be tracked for your students, or rather to be able to track your students with those quizzes, then use one of my canvas exports and really sort of buy into the whole curriculum. And of course that gives you the option to make any modifications that you wish to. So with Quizlet you're finding these, even though these are these are resources that allow you to publish under any license including traditional copyright, allowing you to export them easily here for example in the form of CSV file is really important I think to making sure that our materials don't get stuck in a single sort of piece of technology. And on a certain sense this is actually very personal for me because as I began the project. I had all sorts of ideas but I through the process of learning about all the other open resources as well as some of the materials I myself was creating. I really learned that I had to think more openly about how what kind of materials are good and how I can use them. So, I learned actually in the process that these reality style videos that I created were really also showing us an example of non-normative language. They were using forms that weren't traditionally taught in textbooks. And then I realized that some of these ways that they're responding are actually the keys to how my students for sure is responding so I went back. And I realized that what we need to do is is embrace that what do I really need to do to teach my students to use these forms, or rather to answer these questions. And what I actually go off and say to my students now is, you know, this course really is about answering about 100 questions in check. That's kind of an oversimplification of it, but it's not by too much. The process of learning how to answer these questions about themselves, people around them really leads to them learning everything that they need to do to be proficient in in check. Really, I choose a lot of the grammar and the vocabulary based off of what they need to answer those questions. And so this really the sort of kind of example of reverse design. How do we get to where we want to go while we design backwards for that. And it was also realizing that I needed to include things like non standard check which is so common and every other instances and the interviews that I, that I filmed and created, as well as the content that I was finding on YouTube. All were examples of this common check of this sort of lower variety, but this is important and is often left out of textbooks but I felt that it was really important for my own pedagogy to question these. So we, what are the idea is the ideological basis for leaving these out. One that I really agree with and in the end it's not. And reality really was finding all of this great content that was that is out there and adapting my pedagogy to help my students interact better with with those with those things that I was finding and so, you know when I started off I started off with this scope and and you can see right there in the left the grammar was the most important thing for me and really I abandoned this as I began creating this this curriculum. To one that was more much, much more communicably driven and and as I've been describing really sort of focusing on what did the students need to achieve the order to accomplish these tasks.  I, instead of going to this sort of, you know, I have this elaborate plan that I for what I want to cook tonight, and then realizing maybe there's no tomatoes, or, you know there's some other vegetable I had cooking with is no longer available well, there's still a lot of great stuff out there and so, you know whether it's the open content that I was finding or the, or the materials I was finding through my interviews it was really about embracing that that and being open to that. You know what is out there and how can I use it to really help meet my proficiency goals. In the end, I can say that it has been a really positive experience because I've noticed massive changes in how my students end up their course with in terms of their proficiency gains. So it's overall been an extraordinary experience. So, again, if you want to visit the website is a reality check dot org I hope you'll you'll take a look at it I almost said check it out. And then at this point if you have any questions. I'm going to ask you a question well people are concentrating then. So your, your idea here is embracing open, and maybe you didn't really embrace open completely at first. What do you think was your biggest challenge to overcome. Why did you not like embrace openness originally. And for reasons part of it was, I was hearing that there were these great materials available, but I didn't really know how to search for them. And so there was this one night just searching in YouTube and, and I remember it was. It was like I didn't know about anything and then suddenly I'm able to, I know, you know, I'm finding all this amazing stuff and it was just a really sort of really key moment for me because I came up with, you know, maybe 20 bookmarks in the span of like 15 minutes. I realized though, I mean, I looked at it and I thought there's all this great material out there but then how do I use it. And so I had to really be creative and sort of thoughtful about how could I actually use this, this material. It's really great but it doesn't sort of fit into the pedagogical framework that I've been using the paradigm and been using so let's maybe change that paradigm. Change the paradigm. Alright. Well, thank you so much Christian.


akeiniwai aqia narawe kai teisrūt pāti i, Liida. Judith Collins, aqia pasiria. Aqia pasiria, Corrin! Wadai, Simon Bridges ja izahara aqt. Aqia pasiria, i? Aqia pasiria, narawe mai. Tu sa ko, maa ato tawatai i wakarei, na i huku i kokoa. Na, maa mwai apie pa i kwaytidatia. Aanda aqt, tu i k extractu i, maa pwopi i kajara pa. Aqta, maa ki, Aka, i kajara i, aqtikai i uniti, kuraitai, aa launo maurpunit Police Educ salut wieldung! Dis g생 pareil  warnings uh pasanewe kai wizis ma muleşa Anga b Daily kakaaman shrimp mla plea ap sheets systems ap ap ap ap ap ap ap ap ap ap ap ap ap zadaf one organizumblesunan ira-kalkus a meneida'n i-sau amu kloka. Ngai tata meneida'n aksu akunatama meneida meneida, sy'n panerau sy'n bachuri, ganufili panerau meirai. A mojata tata meneida collectedeya dāghodau o borirau te tanei tata te koja uto atama kialo te pa i fani i i, a meneida tata ka meneida tata. Na, te paru, te dokus, asma uatana tata na, maetano meneida. Achi dada, a peneida, ma cettei Who!" London News NZ at ita sto kanm. So re UM額d, I think we've got to have a culture the national primary they can do that! Pats on Simon Bridges is very straīng forward. As an I am feel that I got no problem feeling with Simon Bridges and I think he is going to be doing a great job. Simon Bridges and I both with reasonably ire positions on your front bench and I see... Simon Bridges this morning already making some comments in the New Zealand Herald suggesting Releision to Todd Muller's leadership coup that he, Kazama Bridges, says, we wasted a bit of time, so, I mean, there's already a bit of sniping there. Oh, I don't think there's sniping. Look, I think it's very important that everybody moves on. I don't like seeing former leaders who have been chosen by the caucus for their clearly leadership qualities and other qualities not respected in the way that I think that they should be. We've got someone like Todd Muller who is, I think, one of the nicest people in politics and very highly qualified in the trade area.  And I just love that and very straightforward deal with the highly intelligent. Well, it's the reality. The reality is you didn't have much choice that you had to put them on your front bench because you've lost 12 MPs, many of them very senior to in one day. People are leaving in droves. Karen, I have always had choices. That is a fabulous team. Do you know what? I'm just so proud of them. And the choices I had, the hardest choices, was who I couldn't put into that top 20 because there are so many people actually who deserve to be there. And I just can't buy them. OK, but you also had a choice with Amy Adams because she said she would have stayed if you'd given her the COVID-19 advisory role. Why didn't you work harder to keep her? Because we don't need a COVID-19 advisory role, although I did offer, as you are very much aware from Amy, a very good position and very good portfolios. She has already announced to her target last year. I respect her decision. She's a good person. I just wish her so much happiness in the future and I think, just get on with it. I'm happy with the team. I'm happy to line up. That's my decision and that's what Leader does. OK, if we look at housing, why is housing so far down at 14? Jackie Dean relatively, well, she's got some experience but not in a major portfolio. Can I tell you, Jackie Dean at 14, that's a cabinet position. Look, Jacinda Ardern had filled twice with housing so how could she take it seriously when Labour had it? And now it's with Megan Woods. She's got about every other portfolio that Chris Hipkins doesn't have. How's that ever going to get any traction? We've got some great people and I'm very happy that I've got someone so... OK, well, on housing, I guess people will be looking for an indication of where National will go with housing after your last nine years. Do you agree with Nicola Willis, who was the housing spokesperson I think last week even, who said that you hadn't built enough state houses, that there was a net loss of state houses during National's last term and that that was a mistake? Yes, she is absolutely right. Absolutely right. What I would also say too is that we waited too long with housing to get those things in place. But I can tell you this, when we left office, there were fewer than 5,000 families on the State House waiting list. Now there's over 15,000. So whatever Labour's done, they've done a lot worse. So you acknowledge that that was a mistaken policy? Well, the policy of selling state houses to those community providers, is that something that you would continue to do? Absolutely. There's a good thing to do. I believe... So where was the mistake then? The mistake was not being able to actually execute enough houses being built fast enough to replace those that were being removed or actually taken out of the social housing pool. OK, so... Also the party that put in place housing first, Corinne. OK, but if we put aside KiwiBuild, which I think we can all agree it didn't go well, will you commit, and people will be interested in this, will you commit to Labour's programme of state home building? The number is 6,500 promised. They're roughly hitting about 5,000 over this term as well. I'm going to commit to social housing, whether it's owned by community housing providers in places like Masterton, where I've seen it working really well, or it's owned by what we all remember as Housing New Zealand or Kaingora. It doesn't matter to me about that. What matters to me is, are people being property housed? Is the landlord doing the job he's supposed to do? And by the way, how can we get more people into either private housing as well, but also into their own home? KiwiBuild shouldn't just be dismissed as a failure. It was a $2 billion flagship policy of an incoming Labour Government and they completely messed it up. Infrastructure, you've got a big announcement due today on this. I know you're probably not going to reveal the details to me. Well, you're welcome to if you want to this morning. But listen, what I am interested in is, what assurances can you give around how you will fund that? I mean, you're going to be borrowing similar levels to what the current Government is borrowing on capital expenditure? You'll just have to wait and see. I'm not trying to tempt me into revealing this and it will be out this morning. I also have a poor goldsmith with me, the finance person I can tell you. Paul is always watching not only the pennies, but also the power. What about other mechanisms? I know you've ruled out tax increases, but will you look at things like congestion, charging, other ways of raising revenue if you're going to build more roads and infrastructure?  We have to wait. All right, well, let's talk about some policies that were announced yesterday. Paul Goldsmith revealing that you would not continue or you would stop the contributions to the New Zealand Superfund. Yes, while we're going through this very difficult economic crisis, it doesn't make sense to anybody who's ever even run a business like I have a household like most New Zealanders have to go and borrow money to effectively put it on a share market. Well, the governments are nothing like households, are they? They've got huge balance sheets. They've got a taxpayer base. We've got a triple-A credit rating, or double-A credit rating. They're nothing like households. And the argument is that if you had continued contributions, when you cut them last time, the rate of return on the New Zealand Superfund was nearly 10%. It would have made billions. These governments are not like households in that way. Governments have to be more responsible than your average household because we have to be responsible for everybody in this country and generations worth of debt. But you also have a responsibility to continue to pay New Zealand superannuation and without that fund building up, we will struggle to pay for the baby boomer's retirement. Well, we haven't seen that at all, actually, have we? No matter what we do, no matter what people think about it, the fact is that we can always start them back again. That's no problem. The fact is, right at the moment, we need to be very assured and the people need to be very assured. We're not going to be borrowing what we don't need to borrow because someone has to pay it back. And that's not just you and me, Karen. It's our children and our grandchildren. And it's not fair to do that unless we know that we're going to invest for their future. Next party leader, Judith Collins. Thank you very much for your time.


Good morning. We will continue with the interaction of the blast wave with a structure which happens to be in the path of the blast wave. For instance, we have a body, the blast wave is propagating. We continue with this and today we will finish this portion namely blast wave and its interaction with bodies. To be able to finish it, let us first sort of review what little we have done in this. We told ourselves, well a blast wave is generated when some energy is released at some source. The blast wave as it propagates further, we considered only a spherical blast wave because this is what really happens when the blast wave progresses away from the source. We have the spherical blast wave moving away from this. We told ourselves near the source or rather in the near field of the explosion, well the over pressure that means if we take this particular point, the pressure rise from the ambient value P0 to the value Ps behind the blast front or the shock front which we call as over pressure Ps minus P0 is rather very high. As it progresses further and goes away far from the source of the explosion that is in the far field, the value of the over pressure Ps minus P0 is small and we non dimensionalized it and expressed it as a value of the non dimensional over pressure. We learnt how to calculate this. We calculated it rigorously in the near field. We said well using some other theories it is possible to calculate it and we arrived at the expressions for this. This is point one. We also told ourselves in addition to this, maybe if I consider a point here or a point here or a point over here, what happens when I look at the pressure behind the front and sort of I say well this is the pressure behind the shock front or the blast front or the lead blast and I express it as a function of time. After the explosion starts that means at time t is equal to 0, I have an explosion taking place. It takes some time for the blast wave to come over here. That means the blast wave reaches this particular point after a certain time we called it as the arrival time and what happens till then the pressure was the ambient pressure and then the pressure rises and then the pressure fell off. Because of the momentum it could go to negative values, we said we got positive impulses. We also got negative impulses. This is the second thing we learned. We told ourselves because of this impulse well the thing could topple down or it could cause its own damage because of the blast wind. Therefore, we talked of two types of damages from over pressure which was crushing or compression because you have rapid compression behind the lead shock and also damage due to the impulse for a body which is hit by this. But then mind you we also told ourselves or we were able to derive something that if the blast wave comes normal over here, you get something like you have the pressure now is P s in the side view. The wave reflects back. Let us see how it reflects back. Well it could reflect back like this. It reflects back over here. The reflected pressure behind it was such that you had the reflected pressure minus the pressure behind the lead shock P s divided by the value of P s minus the ambient pressure was of the order of 8. It is not just multiplied by 2. It could be of the order of 8 for a very strong shock and for a weak shock well it was of the order of 2. Which means when a blast wave hits it normally well I could have the pressure at the surface as a quite a high value that is 8 times the value of the over pressure what I got from the instant wave. This was something which we derived for strong shock and also looked at it for the case of the weak shock derived it for weak shock. And then once it was over we also talked of something else namely we told ourselves well the damage is not only caused by the reflected shock which is very high and the impulses but it could also be caused by the missile effects. Missile effects because fragments from the casing fragments from the neighboring could come and hit it with momentum and that could also cause damage. These were the three types of damages which we talked of. Having said all this we got into the last part and what did we do in the last part? We talked in terms of bodies having impedance and we told well if I have a medium which has a certain impedance let us say medium A having impedance ZA. We have medium B having impedance ZB and we have let us say the blast wave which propagates from medium A into medium B well something gets reflected. This is the incident wave maybe something gets reflected here you have reflected and something gets transmitted into the second medium and we found that if the impedance of the second medium was greater than the impedance of the first medium well the transmitted shock goes away. You have reflected shock in other words I have something like an over pressure coming and hitting this particular interface. This over pressure is reflected back as a shock again we were able to relate the reflected wave with respect to the incident wave and we also found out the magnitude of the wave which transmits into the second medium. But for the case in which I had ZA that is the impedance of the first medium being greater than the impedance of the second medium what happened? We found we were able to derive this expression again we told ourselves well an incident shock comes over here let us say it comes over here it gets transmitted with a higher amplitude into the higher pressure into the second medium but what gets reflected is not a compression disturbance or a compression wave but it is something like an expansion wave that means if I have the ambient pressure here the pressure falls and I have an expansion fan which causes this and this we found is the results in something like spalling of the material A. Having seen all these three or four different aspects of the blast wave let us now go ahead and try to conjecture a little bit more about the damages about the interaction and to be able to do so let us first put down on the board a few cases like for instance we say well over pressure could cause an interaction and damage may be impulse could cause may be the the missile effects could cause and the variation of the impedance change could cause some particular expansion which would cause spalling. Therefore let us first put down the effects of over pressure that means PS by P0 mind you we are still looking at the end view that means we are looking at a shock being formed we are standing away from the shock and looking at the shock and we find that the pressure rise across the lead blast wave is PS or the lead shock wave is PS and therefore we take a few damages we say well a glass pane breaks when the over pressure is of the order of 1 kPa. The next type of damage which can say is supposing a blast wave hits our ear the ear drum ruptures when the value of PS minus P0 is equal to 30 kPa. The next one I consider is brick a brick wall brick wall fails when the over pressure is 50 kPa next a man who is may be standing in the path of the blast wave he sort of tumbles sort of a man tumbles or he is knocked down when the pressure is something like 70 kPa and so on we can keep on tabulating I just put one more or one or two more I say the lung human lung gets damaged when the over pressure is something like 210 kPa and if a human being is in the path like in the path of the blast wave and if the over pressure is of the order of 700 kPa that is seven atmospheres well it is fatal he just dies. Therefore we say these are the things which we can put based on observations of over pressure and let us take a look and why these things should happen and maybe make some recommendation this is what I do today. Having said that let us take the example of glass pane breaking we put this figure on the board again we say well I have a glass pane glass pane is normally thin well I have a glass pane a thin glass pane over here I have air through which may be the blast wave propagates hits the particular glass pane and well the wave gets propagated out let me put the thickness of the glass pane in yellow color this is your glass pane over here well we tell ourselves if the value of the reflected shock behind the pane is about one kPa well it breaks therefore I tell myself well if I consider ps minus p0 divided by let us say p0 well ps minus p0 should be half because I am talking of reflected over here I am considering the value of ps minus p0 is only one kPa or one hundred of an atmosphere and therefore we say well it is 0.05 is sufficient to break my glass pane this is as per the values of the over pressure. Now therefore we tell ourselves well the type of magnitude of the over pressure well if this is the magnitude let us say with respect to the height this is the pressure therefore if I have a small value of over pressure of the order of 0.05 well this is the type of shock wave I have the impulse behind I have the negative impulse here I have i plus over here I have i minus over here this is the type which the blast wave is coming and hitting the particular glass pane. Now let us say for air we looked at the values the value of the impedance for air we said is around 400 to 420 or 440 let us say it is 420 Newton second by meter cube for the glass pane we had a value and the value was around 17 or so into 10 to the power 6 Newton second per meter cube the value for air again was something like we say 420 and therefore what do what do we expect to happen with the glass pane when it is hit by a very small pressure spike of the order of 0.05 that means the over pressure is only 0.05 kilo Pascal that is it hits it I have reflected wave I have 1 kilo Pascal which hits it therefore what is going to happen well on the left side of the boundary I have this which hits it well the impedance over here is less than the impedance over here that means z of the air is very much smaller than the impedance of the glass over here well it gets reflected then as a pressure wave and well if I calculate the magnitude well the magnitude which will be about the same because I find that the magnitude of the z b is very much higher therefore this does not play a role and with the result the some pressure wave gets transmitted into the glass well the amplitude is now twice because you will recall we had the expression p reflected is equal to z b in the second medium minus in the first medium divided by impedance in the second medium plus the impedance in the first medium is a reflected and what was transmitted was equal to p in b which is transmitted is equal to this is the magnitude of the pulse what is coming this is the magnitude of the pulse which is going through was equal to 2 times z b into z b plus z over here therefore with the result the amplitude is higher and we also told ourselves well the glass pane is something which is not very very thick it is quite thin and therefore the thickness of the glass pane being small well this wave does not decay in the small length and when it reflects back over here the ambience over here is again air I have from a higher impedance it goes to a lower impedance value and therefore this wave gets reflected as a reflected wave and therefore you have particles behind the incident wave being being a being in a state of expansion and therefore it is pulled over here here the particles are pulled in this particular direction and therefore the glass material is pulled under tension it fails and therefore it disintegrates or breaks and therefore you find well the glass sort of develops cracks and it breaks but what happens it takes some time for the glass to break and mind you what is transmitted out of the glass is only a very small portion because what gets transmitted out of the glass in this case this becomes the first medium a this becomes the second medium b and what gets transmitted is a very small portion z b being very much smaller than than a than z a what is going to happen the amount transmitted is very small because this is a high value this is a small value very small magnitude of pressures pi gets transmitted into the medium here I have spalling or the glass which disintegrates and breaks but then what is going to happen it takes some time for the crack to develop fully and break by then you have the impulse we told ourselves the over pressure is small and what is going to happen let us plot it out the over pressure you have this is the ambient pressure your pressure rises it comes like this well it goes like this you know since the over pressures are small maybe the breaking can happen in the far field in the far field these things have long impulses and by the time it breaks well the negative impulse could come and if the negative impulse comes the broken glass will sort of fall back over here that means the broken glass falls towards the explosion rather than it falls away from the explosion well this is the type of failure we express we we expect in the case of a glass pin and this is what is observed the glass pin falls back well the over pressures are small in the far field we could have the the breakage of window pins taking place you know we talked of window pins breaking we said in the texas city disaster something over a distance of something like a few hundred kilometers the glass pins of the buildings got shattered and therefore this is one type of failure we can talk of let us come to the next type of failure where we go get back to this maybe we take a look at the eardrum rupture well we told ourselves well you know when we look at our eardrum you know that the eardrum you know we hear all frequencies that means we are talking of the frequency response being quite high for the eardrum if we talk in terms of the frequency response we say well eardrum has a very high frequency response or the time over which it responds to any sound is very small and now if we consider a wave that means we consider an over pressure it is it is coming over here behind the over pressure there is an expansion it goes over here this is the way the wave travels as it moves forward the next signature of this would be maybe at the next instant of time it comes over here the amplitude p s minus p not as decreased well it will go like this and so on it comes like this it goes like this well the the time keeps increasing maybe I should have drawn the second one to be an increasing line because as distance increases the equivalent time increases this was the Kranz Hopkinson scaling law and in this case well it increases still further it comes like this and therefore what is going to happen if this magnitude of the over pressure is of the order of 15 because we told ourselves p minus p not over pressure that is behind a reflected wave that is the total pressure is 30 behind this p s minus p not it is about 15 the air ruptures and why does the air rupture let us again look at the mechanism and then look at the time response the eardrum is a very very thin diaphragm the properties of the eardrum are something like a muscle we can take the value to be 1.6 into 10 to the power of 6 Newton second by meter cube well for air we said it is around 420 or 430 let us say 420 Newton second by by meter cube over here we also find that the value from air the blast wave comes into the eardrum it gets back into the air subsequently the air over here the value is again 420 and what is going to happen well the the blast wave comes over here it meets a higher impedance it gets reflected this is the incident wave this is the reflected wave what gets transmitted is from the from the eardrum it gets transmitted into there may be a small amount gets transmitted but what really happens here within the fabric of the drum you have a wave and behind the blast wave you have expansion it gets reflected over here as an expansion and the eardrum ruptures because of the tensile loading that means if I were to plot if I were to thicken this I have to just take a small part here I say it is the thickness well I have expansion wave behind the shock wave I have expansion wave traveling in this therefore I have this the the particles pull each other and therefore the eardrum ruptures and this is how an eardrum ruptures but then we tell ourselves we also know that the eardrum is a high response system and therefore the movement I have a p s by p not of the order of let us say 15 kilo Pascal that is the total value required is 30 kilo Pascal that means even before the entire impulse is there just the movement the over pressure is there the because of the high frequency response of the fabric of the eardrum well the eardrum breaks we will take a look at the response times a little later in this class but we tell ourselves well an eardrum ruptures from the tensile failure because of the air air and the drum between the type of over pressure is required is 15 from the value of the value of p s minus p not behind the blast wave because the total value of reflected value is twice because the value of 30 kPa corresponds to the far field which is not very very strong well we looked at the eardrum ruptures well if the pressure spike is much larger the reflected shock wave could be not be twice but it could be three times four times up to a value of eight well these are the two cases let us let us look at the third example the third example we take is maybe a failure of a brick wall let us consider this because you know we do use brick walls for protecting structures we have houses in which we have bricks and all that let us take a look at the failure mechanism of let us say a brick wall it could be similar to this except that maybe a brick if it is placed horizontally maybe I have several of these bricks being placed well the length of a brick is around nine inches therefore it could be something like 0.23 meters and this is the brick wall over here we place the second brick over here mind you let us assume that the joint between the two bricks is same as the brick wall maybe it cemented together with same properties let us assume that a blast wave comes and hits it that means I have the incident blast wave and let us presume that we are hitting it we know that maybe the total reflected pressure here if it is of the order of 50 we say it fails let us assume that I have an incident wave whose over pressure that means p0 over here ps over here ps minus p0 is equal to 50 kPa which comes and hits the particular brick wall well the impedance of air ahead of it we take a value which is around 420 we take impedance of air which is let us say medium a before the brick wall is equal to let us say it is 440 let the unit be Newton second by meter cube the brick wall has an impedance and the impedance of the brick wall is 7.4 into 10 to the power 6 Newton second by meter cube and then what is going to happen since the impedance here is very much higher than this what is happening the initial over pressure of 50 kPa gets reflected as an over pressure of 50 kPa that means this is incident this is reflected depending on the magnitude of this well it is not very weak it is not maybe it gets the reflected pressure could be two times or slightly higher than two times over here and then what is going to happen well if I work out using impedances since I use acoustic impedances and we said impedance is equal to the density of the medium into the speed of sound in the medium well I consider the case of weak shock waves well it is just reflected with twice the value that means I have the pressure over here reflected pressure is equal to 50 into 2 that is equal to 100 kPa and this comes out from the expression what we wrote earlier we said well the value of the reflected pressure is equal to zB plus zA into zB minus zA and if we put down the values we have zB is equal to we had 7.4 into 10 to the power 6 minus you have something like 440 that is 0.44 into 10 to the power 3 divided by you had zB 7.4 into 10 to the power 6 plus 0.44 into 10 to the power 3 well this is very much lower than this and therefore this comes out to be equal to 1 and the reflected wave has the same magnitude as the incident wave around the same magnitude. Now we want to find out how much is transmitted into the medium well this is transmitted into this medium this is P into the brick wall B and therefore what is being reflected let us put it down PB prime is equal to we derived this expression 2 times zB divided by zB minus zA well the same thing the value is 7.4 into 2 into 7.4 into 10 to the power 6 divided by 7.4 into 10 to the power 6 0.44 into 10 to the power 6 is almost like zB which is equal to 7.4 around 7.399 into 10 to the power 6 which is of the order of 2 that means I have a pressure amplitude that means let us plot it in blue well this is the amplitude and higher twice this value that means 100 kPa gets you have 50 kPa coming over here therefore the value of the reflected one behind it is equal to 100 kPa and what gets transmitted is equal to 100 kPa gets transmitted into the brick wall well this goes down let us presume for the present that the distance of over the distance of 2 3 meters the amplitude does not get decayed it starts with this in practice over this distance the PB will keep decreasing because as distance moves what did we say as rs by r naught increases the over pressure decreases but in this case let us assume it is a small value and therefore what comes at this interface between the brick wall B and air over here what happens is you have the same value of PB coming over here and when the same value of PB comes over here what is going to happen well it meets lower density a lower impedance air over here which is 440 into Newton second by meter cube and therefore what is going to happen you know the magnitude which gets reflected now has a value you have the value I think there is a sign mistake over here we said reflected over here it should have been ZB minus ZA is a reflected value divided by ZB plus ZA over here and here also it should have been ZB plus ZA and therefore what is going to happen now you have you have the value of B which corresponds to air being very much smaller than the value corresponding to this therefore the reflected wave Pr prime is equal to if I take the value that is going to be 0.44 into 10 to the power 3 minus I have 7.46 into 10 to the power 6 divided by I have ZB plus ZA which was same as the value of around 7.4 into 10 to the power 6 and therefore I find that the similar magnitude gets reflected over here but as a as a rare fraction or an expansion wave rather what comes over here is a strong wave over here it comes over here with an amplitude of 100 and what gets reflected is as an expansion that means instead of compressing it expands over here and since this behind this expansion wave particles move like this here the particles move well the brick collapses over here because brick cannot take tension but more importantly what is getting transmitted what gets transmitted into the air over here if I were to take a look at what gets transmitted let us write it in pink color chalk over here what gets transmitted is equal to what gets transmitted is two times into ZB divided by ZB plus ZA in this case B is the second medium which is 440 that is 2 into 440 divided by this this value is around 7.4 into 10 to the power 6 again is what is and we already know that is 2 ZB we have the value which comes here is something like we said 50 plus 50 is 100 100 comes over here therefore it is equal to 100 over here and therefore you find this is equal to 0.44 into 10 to the power 3 that means it is very small therefore what is going to happen if I have a brick structure housing brick structure and if a blast wave comes and hits it and people are inside the house you know the the transmitted blast wave into the house is a very very small part of what is getting into the brick but however we find that the brick collapses when the when the over pressure which hits it is greater than around 50 and therefore the brick crumbles and this brick can fall on this on the people and cause damage to them but it is not the blast wave which is going to cause damage and therefore when a building falls on on the subjects over here and still causes damage we say that the damage is tertiary that means it is not a direct damage from blast wave but it is rather the collapsed building which causes causes the disaster therefore we tell well the well the type of damages which are caused could either be primary and primary is from the blast wave directly hitting something which causes this which causes the damage it could be secondary in the case of secondary it could be due to missile effects primary could be from over pressure and impulses secondary could be from missiles and fragments which have the momentum and it is the momentum which goes and knocks down a person or or causes injury to the person and the third is tertiary which is due to the effect of a collapsed building on the human being therefore but how do we make a wall which is which is explosion proof or such that we save some people well that tensile strength of the brick or the concrete over here which is used instead of the brick must be able to take tensile failure and therefore we make better concrete systems maybe instead of brick we use concrete and in concrete we put some slag such that the tensile property of the concrete is improved and we if we can now think in terms of a situation wherein we make the wall of the building little thicker well let us put that figure down in fact we have a thick concrete wall and then if a blast wave comes and let us say something gets transmitted into the blast wave we have the incident values P i prime what is get transmitted is let us say twice the value but still it is quite high if my thickness of the wall is something like very large by the time the blast wave comes over here the reflected value depends on the value which strikes this interface between the wall and the air over here and if this value is now decreased from the value of the large value over here because of the larger thickness well the expansion will be very weak and it will not be able to spoil or cause damage to the concrete over here therefore whenever we use a concrete wall for protecting we not only make the concrete to be higher to have higher strength and tension but we also make the wall to be thicker and such type of construction when we when we use for protecting human beings or maybe from blast is known as a blast wall we use blast walls not only for human beings but to protect some equipments maybe we use it in places where we expect a blast wave and this is used as a protection structure well this is about protecting people and human beings and how to go about this maybe I could also think in terms of a different situation maybe I could have steel we said steel has a higher value of the impedance the value of impedance for steel was around 46 into 10 to the power 6 Newton second by meter cube and you know if I can use steel maybe a smaller thickness because steel can take some amount of tension compared to concrete I can also use dual structures wherein I use maybe steel with some other material over here composite structures such that I I I just keep reducing the values of the over pressures and it is possible to use such structures to mitigate the influence of the blast wave mind you see in these things we presume that the structure of the brick wall or the structure of these composite things are static over here when the blast wave hits it they do not relax but if the blast wave maybe if the boundary conditions by which these structures are held allows the way allows the wall to relax maybe I use something like a structure here which moves in this particular direction well in that case my reflected my transmitted wave will be much lower because I have some structure which is moving and when it moves well it it takes it takes it relaxes the type of the it reduces the strength of the wave which hits the particular wall therefore the boundary conditions are important but in this case when I have a wall which is rigid well I can presume that maybe the blast wave comes it I have the reflected wave and I have the transmitted wave and this is what what happens in practice if you want to protect some vehicles maybe I would like the ends if I if I if I want to relax it well the ends the depending on the end conditions the the structure could move if it moves well it it absorbs some amount of shock over here and the transmitted shock will be even lower having said that let us let us go to some other examples let us go to the last example we take and then we will generalize it how about a human being who is struck by a blast wave and because what happens is maybe at 70 kPa we said well a person who is maybe standing at some place gets knocked down what is this knocking down let us take a look at this we take the example let us say there is somebody standing over here well an over pressure followed by an impulse comes and hits him because of this what happens well he he he is because of the over pressure he is just forced he is displaced because of the impulse what is going to happen I give him a momentum I give him a velocity that means he gets some velocity and therefore the when he moves slightly there is some drag force because of the wind effect he is dragged behind and because of the drag force what is the drag force d you have rho v square divided by 2 the velocity with which he is dragged forward the sides are he is pushed in this particular direction into the drag coefficient over here because of that maybe he he is displaced over here and ultimately maybe he falls on the ground something like this that means he is toppled down and why does he get toppled down because of the impulse that is the positive impulse which provides him with a well with a velocity in addition what happens is the over pressure sort of displaces him whereas the impulse maybe knocks him down we said an over pressure of 70 kPa is something which knocks him down well it pushes him and the impulse behind it knocks him down therefore maybe in this case I should consider the failure or the or the type of destruction or the knocking down is more due to impulse than it is due to the over pressure the over pressure will only displace him like like like for instance let us consider a man who is stout who is heavy who is hit by a wave well he can withstand the over pressure but as he is dragged down by the by by the velocity by the by the blast wind well he topples down therefore let us try to put this in in a in a better scenario I I show it in a particular slide you know I show here an object over here and this object is being hit by a by a blast wave over here it comes inward it hits him over here when it hits this particular irregular sized object over here well it gets reflected well the reflected pressures are very much higher than the incident values depending on the strength of the initial blast wave what we get and well the reflected blast wave moves outward in this particular direction because the object is not very very much like a straight line or something which I have assumed over here maybe I have the initial spherical blast wave coming over here the characteristic length here is small and therefore I represent it by a straight line you know because of the reflection you know you have uneven pressure distribution on the surface and therefore you you have the loading on the on the on the particular body over here is not very even in addition to this what is going to happen the blast wave when it comes in these particular portions it gets expanded over here the blast weekends and far away well here it could still be stronger near the body it weakens and it progresses over here therefore you have higher pressure here lower pressure here therefore maybe there is some wind over here therefore what is happening as the wave moves forward maybe you are from the higher pressure region towards the lower pressure region some wind blowing well it creates an eddy or a or a vortex over here I have a vortex over here and the blast wave ultimately which moves through the air gets here there will be some element of transmission of the blast wave through this we have not put this in this figure but what I want to show is well I have the velocities which are induced over the surfaces and they cause the drag and because of the drag well the body gets knocked down and this is the thing but what is more important is well the blast the over pressures over here need not really be even and you find that the body is subjected to over pressures here which are not of the same magnitude because of the distances here the incident wave is a little weaker than the wave over here here the incident wave is stronger because it is nearer over here and therefore we find the pressure distribution over the body is itself not not uniform here you have expansion taking place and because of this you have a force over here which in addition to the wind causes the body to be knocked down therefore what is it we can now summarize the whole thing by telling the following well we looked at three or four examples and based on these examples we find well both the over pressure and the impulse that is the wind effects are important but can we say a little bit more we also talked in terms of the eardrum having a very high response that is the response of the human here is so small that it is a very small number and therefore we said well it could be due to the over pressure itself impulse will not play a role because even if I have a short impulse well it the impulse is over a period of time much before this time well the ear ruptures because it is thin and the reflected expansion waves at the second interface causes the failure therefore we know we have to somehow relate the time of the impulse that means we are talking of positive impulse t plus we are also talking in impulse over here t plus with respect to the characteristic time that is the frequency response of the body which I can say is tau I can tell well the eardrum has a characteristic time tau which is a very small number whereas the impulse has a characteristic duration let us say t plus or some value of t over here how do I relate these two is the question therefore to be able to understand this let us take one small example of let us say a structure or some particular body which is resting somewhere and we all know well it is possible to represent a body let us say of mass m and you know there it is resting against some place therefore I can also model it in terms of a spring mass system well I say equivalently I have a spring of stiffness k and it is held may be over here and what is going to happen well it is hit by a blast load therefore I have something like an over pressure and behind it I have the impulse coming over here and what is happening is I have the pressure initially is p0 rises to ps then it comes to p0 again and it reaches the value of p0 again this is the positive impulse this is the negative impulse therefore because of this at different instance of time I have different pressures which the body forces or rather I have a force as a function of time or rather I can tell myself the force which the body experiences is when the lead shock may be at this particular time when the lead shock comes over here well the force reaches the maximum and thereafter the force decreases and therefore this particular characteristic can put as in terms of force being varying with respect to time. Now therefore I have a periodic or a time dependent force striking a body of mass m which has some in it sort of a spring over here some value of holding the body is here therefore I can represent this free body diagram of mass as m I can say well if I consider spring of stiffness k then I have k into x over here which is the resisting force I have the body force over here ft I have the force that is the force on the free body diagram it is m into x dot over here this is that let us say the direction of x over here this is the acceleration and therefore I can write my equation for the body as equal to mx2 dot plus kx is equal to the time varying force over here and now if I look at the frequency response of this particular body well the frequency is equal to under root k by m stiffness by the mass of the body well stiffness as units of let us say Newton per meter body has units of so much kilogram m as units of kilogram therefore you have Newton per meter kilogram over here this is equal to kilogram meter per second square this is this is therefore equal to I have kilogram meter per second square is Newton I have meter over here therefore this becomes therefore the unit is one over second and this is the frequency so much one over second and if I look at this characteristic frequency the frequency is very high well the the the characteristic time of response of the body is small and therefore if I have a body which which has a very small response well the over pressure itself is sufficient to cause the damage whereas if the characteristic time t of the body is large what do we mean by large large as compared to the or significant as compared to t plus well the impulse will cause a damage and maybe what is going to happen is the average value of the pressure is going to what is going to cause the damage plus the impulse is going to cause the damage can I therefore put these things together in some form of a figure such that I illustrate where impulse is going to cause a damage where over pressure is going to cause a damage let let us try to see whether I can do that what I do is I have a figure in which I put over pressure on the y axis that means I put p s minus p not over here I put impulse on the x axis well you know for some bodies we find that well impulse is really not a matter of concern it is only the over pressure which causes the damage because the response is small therefore I say well this could be one one one case over here and this particular region is the region wherein only over pressure type of causes the damage I could also have the other condition wherein I could have something like a large value of impulse which causes the damage maybe even at smaller over pressure I could have large values of impulse which causes this therefore this becomes my second zone over here therefore what is it you know we are talking in terms of a situation wherein maybe this is the limiting asymptote corresponding to impulse therefore I say this is the impulse asymptote well here it corresponds to the minimum threshold value of over pressure or over pressure type of an asymptote over here and what is going to happen this happens in this region we tell that the characteristic time of the body tau is of the order or very much greater than the impulse time that is t plus or equivalently the impulse time in this case t is very much smaller and in the region wherein you have t of the order of magnitude that means the characteristic time of the impulse and the characteristic time of response of the body are the same well it could be the dynamic region in which case I have to do the dynamic analysis that is the dynamic range over here and therefore if I were to put the value of let us say an iso damage line for both over pressure and impulse what is it I will get I will get the value as something like this coming over here and coming over here and this becomes something like an iso damage curve therefore we could talk in terms of maybe impulse induced damages when the frequency is large or the characteristic time of the body is small of response of the body is small we talk in terms of these damages here when the time constant of the body is quite large compared to the impulse times and when both are of the same order maybe we should do some dynamic analysis or this is the dynamic range of this and to do this is quite involved maybe we will have to look at the frequency response of the bodies and put together that over pressure and impulse together well this is how we look at damages and let us continue with this let us take a look at what are the type of impulses which we get on the body and the ambient and how they amplify each other we will consider one small example now let us revisit the example of crater which we talked earlier we talked the example of a crater what happened in the case of a crater let us put it together you know in the case of a crater we have a blast wave which comes towards the earth well the blast wave hits the earth gets reflected goes up and we also talked in terms of additional waves which are being formed let us take a look at it well this is the earth over here well a blast wave originates from let us say air over here blast wave comes over here strikes over here then what happens something gets reflected let us take a let us plot the value of the reflected values well the reflected wave comes over here now we told ourselves well the reflected pressures are higher and therefore and the these reflected waves are traveling in a medium which is already heated by the incident wave plus if there is an explosion the other heat from the explosion is also going to heat the medium with the result the reflected waves travel faster and they are even stronger and with the result when these reflected waves impinge on the earth over here if the angle is quite small well I get the reflected waves over here but as this angle becomes shallow what happens is I am not able to maintain you will recall we did this in our class we told well if the angle is such that it is not we are not able to meet the conditions wherein the velocity on the ground has to be parallel to the ground well the the incident wave that is the reflected wave which strikes it gets spurted up from the surface and what I form is something like a mark stem shock and then I have a shock like this therefore I have a mark stem shock a reflected shock an incident shock and of course as all of us know we have the transmitted shock into the ground which forms the crater now we will not look at the crater formation we have looked at the what is it he is going to see what is the type of shock pattern or the impulse pattern he is going to see well let us sketch it out well we tell ourselves I am looking at P minus P naught divided by P naught this is the pressure to which he is going to be subjected to well at this time after the blast wave hits the ground after some time he sees only the ambient pressure and after a particular time what does he see he sees well the wave is going to go and hit him he sees this particular mark stem shock or the reflected shock which comes and reflected shock from the reflection which comes and hits him and then after some time well the second shock comes and hits him and may be so on the third shock goes and hits him and therefore the type of impulse what he sees is not going to be a single spike which came down like this but a series of spikes and in general the impulses because of the ground reflection the other shocks which are there cause a series of spikes in the impulse pattern and we seldom get an impulse pattern which is really something like this but we do get spikes over here because of the additional shocks which come sometimes these spikes could be even larger than the initial value it all depends on the ground conditions on the type of reflections what you have but we must also remember when you have an incident reflected pressure over here at the surface you could have the seismic wave and this wave is also traveling along the surface but what causes the damage is the impulse from this particular one well these are about the different ways of looking at it just to wrap up the subject what I do is in the last one let us take a look you know these multiple shocks in an impulse are not only due to let us say due to when the blast wave hits the earth it could also be let us consider the last example wherein I have a sphere and in the sphere let us say this is the sphere gets exploded that means the initial volume of the sphere let us say we put it back in terms of what we learnt we say that the radius of the sphere is Re a sphere which explodes and when the sphere explodes what happens is a blast wave takes off over here now this is the high pressure gases which explode the cylinder it could be hot it could be cold but all the same it is high pressure and then the interface of the high pressure will also follow it will also expand out like this the high pressure gases expand over here and when I create an explosion that is a blast wave in this particular direction well here the gases are at high pressure and what is going to happen a wave is going to travel back that means an expansion wave is going to travel into the body into the medium which has just exploded and because of this interface over here this is the symmetry line well this reflection wave this expansion wave which gets reflected is again coming over here and I have a reflection wave going over here and now what is happening the dotted line red may be I will show it like this in this region well this is a high pressure gas region which is gradually expanding out this is the ambient pressure over here I have an interface here well the impedance of this is lower than the impedance of this therefore the rarefaction or the expansion wave you know when it comes here well it gets reflected as a shock wave for the same reason you know when a shock wave comes it gets reflected as an expansion when a rarefaction wave comes it gets reflected as a shock wave let us show it in yellow thumb that means it gets into the medium as a shock wave over here well it gets again reflected as a shock wave and therefore what is going to happen it progresses into the medium over here it goes into this medium well over here I get a rarefaction wave or a wave which is an expansion wave and therefore when this comes as an expansion wave over here well you know it gets reflected as a shock wave and therefore I have a wave like this and this wave comes forward and therefore I have a series of shock waves one shock wave two shock wave three and therefore if a person is standing over here or maybe at some particular time he is over here he sees the first wave then he sees the second wave and then he sees the third wave at the nature of the impulse what we see is this is the positive impulse and this is the negative impulse therefore the impulse need not be something which is smooth like what we said it could contain a series of shocks one after the other and this happens in all explosions the interaction between a blast wave and a body placed on the path we looked at the mechanisms of failure and maybe with this we will stop our discussions on blast wave we will revisit it again when we look at ideal and non-ideal explosions and also look at how to quantify damages we will try to quantify damages in term statistically because we also recognize that we told ourselves in this class that may be the eardrum ruptures at let us say a pressure of 30 kPa may be a small child who is more sensitive the eardrum of the child may rupture quite early because still very tender whereas some an older person will be able to a strong person might be able to withstand a pressure of 50 kPa therefore to some extent the damages are statistical in nature and therefore later on in the course we will look at damages through a statistical procedure well then thank you and in the next class we will try to take a look at energy released from the explosion in explosions thank you and announcement please in the last 12 lectures we have covered the basics of what constitutes an explosion and the modeling of blast waves I give in the downloads of this video course additional reading material namely references relevant to these portions a small set of homework problem is also given to help you work with the basics which we covered in lectures 1 to 12.


Welcome to Recall Roundup, check to see if you have any of these recall products in your home. Kitty Land is recalling about 12,000 of these Disney's fairies plastic racing trikes. Now, they're a laceration hazard to a child if the child falls on it, and there has been an incident like that. They sold for about $50 at Target between July and December of 2009. If you have one of these, take it away from your child immediately, contact Kitty Land and Kitty Land will send you a free replacement handle bar. Under Armour is recalling about 500,000 of these chin straps for football helmets. Now the metal snap that connects the helmet to the chin strap is very sharp and when it comes in contact with another player it can cause a laceration. There have been six reports of injuries that required stitches. Now they were sold for about $20 at Sporting Good Stores and Under Armour Outlets. If you have one of these, contact Under Armour for a replacement chin strap and that's free. Family Dollar Stores is recalling about 160,000 of these animal sock top slippers.  Now they were sold at Family Dollar Stores for about $5. If you have these, take them away from your child and return them to any Family Dollar store for a full refund. And finally, Michael Stores is recalling about 28,000 of these Ashland glass vases. They are a laceration hazard because they can break or fracture when they're picked up. There have been reports of one person requiring surgery and two others requiring stitches. If you have one of these vases you can return it to Michael's for a full refund. That's Recall Roundup. You can go to our website, SaferProducts.gov to find out more about these recalls and others.


Hi, I'm Zor. Welcome to Unizor education. I would like to spend some time basically proving some theorems, which I present as problems on Unizor.com. So these problems are related only to the material in solid geometry, which we have already covered, which basically are lines and planes parallel and perpendicular to each other. So, just a couple of very, very simple theorems, which are presented here right now, and I would like to be as rigorous as possible. So it might actually take, I don't know, maybe a little longer, because the theorems are actually relatively trivial, but I would like to be precise as much as I can. Okay, now the theorem number one. If you have two lines, A and B, which are parallel to each other, and you have a plane, so this is a plane, and these are lines. And you know that one of these lines are perpendicular to the plane. Well, it's kind of obvious that another line also should be perpendicular. So this is your A line. This is your B line. So they are parallel to each other, and I know that A is perpendicular to the plane gamma. Let's connect these points. This is the base of the perpendicular A, and this is the point of intersection. Now, by the way, here is one simple kind of deviation towards precision. I said, okay, B is a point of intersection of line B and plane gamma. Does it exist? Maybe they don't intersect. Well, let's just think about it. If B does not intersect gamma, then B is parallel to gamma. Now, A is parallel to B, and we have already proven before in one of the lectures that if you have two parallel lines and one of them is parallel to a plane, then another is also parallel to that same plane. And if A is parallel to plane, there is no intersection, and there is no intersection cannot be perpendicular, obviously, right? So just a little detail, which in many cases is just completely missed. People are just saying, okay, let B be the intersection point of line B and gamma. We have to think about existence of this. All right, fine. Now, to prove that B, line B, is perpendicular to gamma, I need to prove it's sufficient to prove, again, not I need to prove, it's sufficient to prove another precision point. It is sufficient to prove that line B is perpendicular to at least two lines on the plane, which are passing through the same point of intersection. Well, let's just think about this way. A and B are parallel. From the definition of the parallel lines, they are supposed to line the same plane and have no common points, no intersection. So A and B do lie in the same plane. Well, let's just draw that plane somewhere here and basically points A and B belong to lines A and B correspondingly and the segment A and B would be an inter... belongs to intersection of this plane which goes through A and B and the plane gamma. Why? Again, because point A belongs to both line A and point gamma, right? And therefore A supposed to belong to this plane as well because it goes through the A. So that's why A is an intersection. Same thing B. B is an intersection between line B and plane gamma. Now line B belongs to this big plane. Therefore, point B belongs to both this big plane and gamma which means it belongs to intersection. And again, being as precise as possible, I can remember that if two points belong to intersection of two planes, then the line which goes through them also belongs. So the whole segment A and B belongs to the plane gamma. Now obviously within this plane which now contains this line, this line and this segment as well lines A and B are parallel. Now, I also know that this angle is 90 degrees because A is by the condition of the problem is perpendicular to the plane and therefore it's perpendicular to any line which goes through A. So I have this perpendicularity. Now on the plane, if you have two lines parallel to each other and you have a perpendicular to one line, it will be perpendicular to another. That's from the plane geometry, which we all know. Which means that this angle is also 90 degrees. So line B is perpendicular to segment A and B or line which goes through the segment. Okay. Now that's one. Again, you remember it's sufficient to prove the perpendicularity of the line to a plane. It's sufficient to prove its perpendicularity to two lines on the plane gamma that goes through the point B. We found one line. How about another? Well, it's also kind of simple. Let's draw two parallel lines through A and B. And now let's compare. Let's say this is A prime and this is B prime. Let's compare angle. We need these points as well. C and T somewhere. Angle C, A, A prime and angle D, B, B prime. This angle and this angle. Now, by construction, A, A prime is parallel to B, B prime. By the preposition of the theorem, C, A is parallel to D, B. So these two angles are angles with correspondingly parallel sides. And therefore, they are equal to each other. We know that from the plane geometry, if you have two angles, it doesn't really matter whether they are in space, separated or in the same plane. We can always bring them to the same plane if you really want to. But as long as the parallel lines, the sides are parallel, then the angles are equal. So this one is 90 degree because the line perpendicular to any line, A is perpendicular to any line on the plane, which goes through the point A. And therefore, this is also supposed to be 90 degrees. This is my second line. Well, actually, kind of similarly, instead of using this line, A, B, I can immediately draw two lines here and two parallel, correspondingly parallel lines here and just deal with those angles. It doesn't really matter. Okay, so that actually proves that line B is perpendicular to the plane gamma. We found two lines on the gamma, which goes through the point of intersection B, which are perpendicular to the line B. That's why there is a perpendicularity. Okay, that's my first theorem. The second theorem is kind of an opposite. If you have two lines and both of them are perpendicular to the same plane, plane gamma. So in kind of, yeah, it's kind of a reverse. So you have a plane and you have two perpendiculars, one and another. We have to prove their parallelism. We have to prove that A is parallel to B. All right, so if these are two perpendiculars, these are two bases. What I will do through the point B, I draw a line parallel to A and I assume, let's call it B prime. I assume that this line is not the same as line B. So what happens? From the previous theorem, I know that A and B prime are parallel, which means that from the previous theorem, B prime is perpendicular to gamma. Since A perpendicular to gamma and B prime is parallel to A, then B prime is perpendicular to gamma. Just the previous theorem. So what happens is at this point, point B, I have two perpendiculars B and B prime from the plane gamma. And that is impossible because we have already considered the existence and uniqueness of the perpendicular from the very beginning. Whenever I just introduce one of the first lectures, I think the first lecture about line perpendicular to the plane, I was talking about existence of the perpendicular and their uniqueness. So this contradicts the uniqueness which has been proven in that lecture. So which means that B and B prime are one in the same line, which means that B is parallel to A because B prime is parallel to A by construction. So that's my second theory. Very simple. I just use the first one as the basis. Okay. And the third one, which I wanted to do today is if I have a plane, point M outside of it, and I have two lines A and B. So I have lines A and B. Their intersection is point M, the intersecting M. And I know that A is perpendicular to gamma. So I have a plane gamma. So what I have to prove is, now A and B are two different lines. I have to prove that B is not parallel to A and B is not perpendicular to gamma. So one is a perpendicular and another is something else, which is crossing the gamma. I did not really specify that, but I have to specify that B intersection gamma is not empty. So there is point of intersection because if there is no point of intersection, I can put B parallel. But I'm claiming that B is not parallel to A. I can put parallel to gamma. So all three conditions. B is not parallel to A, B is not parallel to gamma, and B is not perpendicular to gamma. Okay. How can I prove it? Well, some of them are very simple. Since B and A have a common point, B and A cannot be parallel. Since B and gamma have common point, the intersection, B cannot be parallel. Now, how about B being not perpendicular to gamma? How can that be proven? Well, very simply. From the previous theorem, which I have just proven before, if you have two perpendiculars, A is perpendicular by the preposition. And if I assume that B is also perpendicular, then I know that both will be parallel to each other. I just proved it second together. But I know that they are not parallel because they have point of intersection, which means this cannot be perpendicular. You see, I actually proved only one theorem, the first one. And the second and the third were very, very easy consequences from the first. Well, basically, that's it. I do recommend you to try to do exactly the same as I did, just by yourself. And what's very beneficial, I cannot really overstate all the good benefits which you can get from this. If you can write down the proof, whatever I was just explaining, if you can write it down on a piece of paper, rather than just thinking about this, it would greatly improve your understanding of the whole logic. Because whatever you are putting down on paper inculcates into your mind significantly better than if you just think about it. So that's my very, very strong suggestion in this case. And to tell the truth for any other thing, whatever I'm just proving or solving or whatever I'm doing here, if you can try to replicate it after the fact, after you listen to the lecture, just buy yourself on a piece of paper with as much details as possible. For instance, if you remember, I paid attention. Okay, let this be a point of intersection. Is there a point of intersection? Something like this. So try not to miss any piece of the proof. Try to make it in such a way that nobody can answer why. I mean, if you, for instance, said, okay, this is the point of intersection, somebody can ask you, why do you think they intersect? You see? So nothing should be left without the proof and put it in a paper. And, well, let me warn you, it will be a lengthy kind of a composition. But it's worth it, really. That's it. Thanks very much and good luck.


For 1963, the kills in this movie are MWAH! Oh, they're fuckin' great! 80 Slasher kills! 20 years before, there were 80 Slashers.  Hitchcock couldn't even go there for Psycho! Three years later, they can show heads coming right off and rolling away! Ahead of its time, in more ways than one, we really think this is the prototype to 80 Slashers. Axe Murderer, you got good kills, 80 Slashers, like, he's gonna get it! You know he is! The bumbling idiot! But when is he gonna get it, that whole like... I can't think of a movie before this where that kinda happens, where you're like... Yeah! Yeah, you know it's gonna come.


How's it going guys? It's Justin today. We've got a brand new trailer reaction to do John Wick chapter 3 Parabellum. So excited to see this trailer Look at Neo and all those Smiths. I mean look at John Wick and and all those assassins anyway Awesome trailer awesome poster. I mean we're about to watch the trailer ready three two one. Let's go From the foot the last movie Puppy Trailer for Houston Was that a keymaker? From matrix. I love the lighting swords Yes, I used to book horse gun No, it's not double-dog action That's really awesome. That's very awesome It's it's a great tone trailer. You definitely get the sense of what the movie is gonna be about He's on the run and they've given him time. So at 6 a.m. I'm assuming he has to run and I don't know Just how is it gonna get out of this he can he can take down some guys but 14 million dollars, I wonder why specifically 14, but 14 million dollars is a lot of money especially for all of these guys to want to have a piece of and I wonder if during the film a bunch of them are gonna be like, well My loyalty to you John versus the money. I Wonder if the I wonder if there's gonna be that that dynamic at play Still don't really know what Halle Berry's they're doing especially maybe she's an old accomplice or Partner of his an ex of his probably not But yeah, just I'm I'm excited to see where it's gonna be going anyway guys What did you think of the trailer? Let me know in the comments below While you're in the comments look for that subscribe button if you haven't already hit that and don't forget to like the video and Yeah, subscribe as well hit the bell notification that'll really help us help us out a lot anyway guys Thank you so much for watching. My name is Justin and until next time. I'll see you at the moon


Viva el mariachi! Viva el Cinco de Mayo! Among all the economic indicators that seem to evidence that recovery is at hand and that we're having recovery the most significant one is kind of being ignored and that is that our critics aren't calling unregonomics anymore. It must have been sometimes when you said to yourself I had a chance, boy, would I ask him? And now we do have a few minutes here and go ahead. Any questions or any questions? People are pretty well satisfied. I want to tell you how very proud we are of the job you're doing and that we care very much for you and Ohio. We hope you'll come out to Ohio a lot more. We hope you'll run again and we're very proud of the job you're doing. Well, thank you very much. I appreciate it. One comment is present out in the field with the grassroots people. They are really excited about the fact that you haven't backed down that the things you said you were going to do and the stands you took you're still right on top of and holding firm, right? It's significant for the people of Ohio. And then more compliments, everyone. As I've said, Bob Hughes is in Death Valley, in Kylewood County. Mr. Farmer can stick with him. That is from the head of the Republican Party in Kylewood County. Well, I have to say I appreciate that very much, but I just want to assure you that one of the advantages at least of my age, what point would there be in changing that? Sir, I was with campaign 70. You noticed I'm not speaking to that thing that you so very kindly said. I think that if anything would be wrong, you could automatically become a lame duck. And the other way, if you said the other things, you could automatically find yourself a target being opposed on everything you wanted because they would then say it was political campaigns. And Mr. President, just an extra kudo to your sending George Schulz into that cauldron in the Middle East with that successful agreement and leading to some others out there. Well, he's going to get home Wednesday afternoon and I know the cable traffic back and forth, and I sent one cable to a cemetery with an explosion over there. Since the terrible tragedy of all it was there, I couldn't resist. I sent him a cable with the river ahead and said, don't forget the duck. In the hours, they really, those people do like long meetings and he's been on the schedule and it's just unbelievable. And winding up in Paris for a general meeting there and a whole different subject than with our European allies. But some of these meetings, far into the early morning hours, like seven and a half hours of meeting and discussion. And I think when I say hello before I even welcome anyone to apologize for what he's been put through, he's great, he really is. Mr. President, I'd like more John Wolf. You know, in so many communities you have publishers that like to publish their own opinion. Here is a man with his own money stands back at you and the Republican Party, the publisher and the owner, to come with this bet, about 350,000 on Sunday. And they're the leading Republican paper in the state of Ohio. Period. My friends from London last year and I'm pleased to give him where he goes. Well, listen, that's a good... They have to wake up every morning with a wash and a post. When news is still with us. Yes, Dave Thomas. You're doing a great job. Mr. Tony will tell you that too. Yes, I saw it. Well, you are doing a fantastic job. The city is seeing you, sir. I'm very pleased to see you in here. The general? For me too. Sir, I just want to add, the Rubens know what a wonderful job you did, a great job of going down and selecting Jack Bessie as your chairman of the Joint Chiefs. A tremendous person and not very many White Houses would have found him to put him in charge. And he is performing nobody. Brilliant man. The Chief of Staff, the Joint Chiefs of Staff, Army General. He was an enlisted man in the Danseal Beach. Yes, sir. A battle field commissioner from World War II. No, he's just great. And all of the Chiefs are... Very moral, man. That's strong. Incidentally, on this defense buildup, there's been so much taking on us as if this old kind of a perception that people have to make sense of it.


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The first thing we must recognize really are the achievements that have been there materialized since the Good Friday Agreement and really the measurable changes on the ground and in parallel we see a number of residual elements of violence that continue to affect a life and whose humanitarian consequences are a matter of concern to the ICRC. I think here of the impact of punishment beatings but also the protests in places of detention, unresolved cases of disappearance and missing persons. So these are things that have triggered a renewed interest and focus on the part of the ICRC, particularly in engaging with individuals and groups including marginalized groups on the consequences in humanitarian terms of some of these issues. We are supportive of a number of grassroots and community organizations that engage on issues of the attempt to mitigate violence such as in the case of punishment beatings and we're supportive of some of these initiatives. We're also supportive of efforts that are underway to try and resolve some of the pending cases of missing persons and we also have an agreement with the Ministry of Justice on the ICRC providing insights, observations and findings and recommendations on the situation inside places of detention. These are not the traditional types of visits that the ICRC is known for internationally but it's a way of collecting elements from a variety of individuals and groups that are related to prison regimes in order to formulate recommendations and observations that can be helpful in addressing some of the more problematic aspects of it. And finally we're also supportive of the work of the British Red Cross in terms of youth and education but also of their wider role in Northern Ireland. This phase of our engagement in Northern Ireland we're in an early stage but certainly what is clear is that the ICRC is imperative in humanitarian terms the way in which we approach a situation, the neutrality, the independence of it, the fact that we can engage across a wide spectrum of individuals and groups to try and provide solutions that would address some of the humanitarian concerns in the context. Those are very very similar from one context to another and that's the driving force behind our presence. I'm absolutely convinced that the ICRC is an organization that learns from practice so we are confronted with very different realities in different parts of the world that we operate in Northern Ireland will help also in that sense to provide again new insights for example into how we address the issue of missing persons or unresolved case of missing persons, how we address certain issues of long-term consequences of a very polarized situation that may have occurred in the 70s 80s and that we see now having ongoing impact in certain forms and that we can help address some of these issues on one hand but also draw lessons for ourselves as absolutely something that will take place also