Thursday, August 17, 2017

Everyone knows Mechanics

 My daughter in the waiting room at the Dr's office...

We all learn Mechanics from a very early age.  The same could be said for much of the sciences.  We just come to know it in a very hands-on way.  The challenge for science educators becomes taking that practical understanding and leveraging it towards a strong theoretical one.  Physics does not live on paper - the analysis students must master is arrived at in a more organic way when it reflects the real world it exists in.

Summer 2017 Projects

Here were my two summer projects for 2017...

1.  My fence.  Two posts dug by hand and two long spikes hammered in.  One interesting challenge was removing the old worn-out fence that was in the exact same location.  A post requires something like 600 lbs of lift force in order to remove it due to the concrete at the base.  I drilled a large hole through these posts, inserted an old bench press bar, and pryed them up.  The bar bent, but it did the job.  Yay torque.

2.  My kids' tree-house.  I had at least as much fun making it as they do playing in it.  I propped up an old 3 by 4 foot pallet about 4 feet off the ground and built around it.  Requires a circular saw, a bench and a drill...and about 300 bolts.  You can see it in the corner where the two fences meet.  I also built a couple of obstacles for my kids who are training to be American Ninja Warriors, despite being Canadian citizens.

That Time I Nearly Died

My scariest moment in recent memory involved the most dangerous piece of home equipment: the ladder.  I have since discovered that a 12 foot ladder should be supported in three places while in use.  Go figure.

I have chainsawed through numerous small trees and long branches, but this one was different.  I needed to make a cut about 16 feet high - otherwise, the falling tree would have snapped the telecommunication wires.  It is not recommended to use a chainsaw while perched atop a ladder, but gosh darn it, the tree cutting company I called told me I would have to wait 5 weeks for them to do it, and I had a tree-house to build...

The tree in question was some sort of weed tree, with an 8 inch diameter, about 40 feet high and leaning significantly.  I leaned my 12-ft ladder up against the tree I was cutting.  Now that might sound stupid, and it turns out it is, but hear me out.  The ladder's friction contact was a couple of feet below the cut point...

With a friend at the bottom of the ladder (like he could actually do anything from there besides have a great view of my demise), I stood on the second to top rung of the ladder, leaned forward with two hands on the chainsaw, and began to cut. With the cut 80% the way through, I heard a snap, which is expected.  What I did not expect is that the cut would cause the portion of tree BELOW the cut to split in half.

I am 12 feet in the air, with two feet on the ladder, two hands on a chainsaw, and I am going for a ride.  The ladder revolved about its base by about 15 degrees (I descended a few feet) until, thankfully, it made a firm contact with the tree somewhere else.  I, in a state of shock, slowly scaled the ladder back down to the ground, and confirmed that all of my body parts were still present.

In hindsight, even had the tree not split, the situation is still far from safe: when the upper portion is cut off a hanging tree, the lower part that is not cut is suddenly supporting less weight, and could shift its angle accordingly to a new equilibrium position.

Next time, I will attach the top of my ladder to something solid with a rope before making such a cut, or, more likely, I will wait for the tree cutting company to do the job for me.

Wednesday, September 7, 2016

Space Elevator Operator

A couple of years ago there was a student in my Mechanics class named Ivan Miloslavov.  He was that one in a thousand kind of student who had
1.  a knack for math and science,
2.  an interest in math and science, and also
3.  some particular skills - in his case, computer programming. 
This trifecta can produce some amazing things, and I want to share one of them with you.

During his time at College, we collaborated on an app called "Space Elevator Operator" (click here to try it...the link will also have a permanent home on my space elevator page).  I am really proud to have been involved with its creation for several reasons, but one of them is that I got to witness a young brilliant student putting his skills to work to produce something tangible and useful in the real world.

The app allows users to simulate placing payloads into Earth's orbit with a space elevator.  It serves two main purposes: 
-The app allows one to quickly demonstrate how a space elevator could work. 
- It is an educational tool that is useful for introductory physics students to learn about orbital mechanics.

One other thing this app does is give all of my students an idea of what is possible if they put their minds and efforts towards something.  The Space Elevator Operator app was shared at the 2016 Space Elevator Conference in Seattle this past month.  It was also recognized by ISEC (the International Space Elevator Consortium).

I wish Miloslavov much luck in his academic and professional future, and sincerely hopes he looks back at his experience on our little project with pride.

Sunday, March 6, 2016

I'm Off Blogging for MakerBloks

Hello my science peeps.  I have been absent from my blog as of late because I have been 'acquired' by another blog, that of "MakerBloks".

MakerBloks is a company specializing in hands-on science education for ages 6+.  The nature of my posts will be a bit less about physics content, and a bit more about science education for kids.  To see my first posting at my new 'home', follow this link.

I may pop in occasionally on The Engineer's Pulse and will certainly keep the blog active and moderate the comments.  Thanks for reading!

Thursday, January 14, 2016

The Martian is a Scientifically Sound Oscar Contender - Almost



Monday, November 9, 2015

I Am Seeking Your Advice on a New Project

I have been blogging about science for five years without asking for any favours from my readers.  Today, I want your advice on something.

Why you?  The fact that you are here, on this site, means that you are probably science-minded and thoughtful.  Perhaps you also value the communication of science ideas.  Finally, maybe you are the type of person that would like to discuss science and engage in experiments and design in a casual setting with family, friends, and even strangers.

Over the coming year, I would like to develop a new kind of workshop.  At this point, I have a vision for what it might consist of, but the details are a blank canvas.

The workshops that I envision could take place in a library or school, perhaps once a week.  Each workshop could have a theme, and would entail a presentation, discussion, experiment, or design, or a combination of these.  I foresee groups of four to six people interacting in a relaxed setting.

I am looking for your advice for such a project.  Should there be recommended age groups?  Have you already participated in such a thing, and if so, what was good about it and what wasn't?

Why am I doing this?  For a few reasons, but the bottom line is that I don't think there is a place for families and friends to do real science together.  It seems to me to be an underserved market.

If you have any comments, please leave them here, below.  If you are in the Montreal, QC area and would like to be involved in the creation of or attend such a workshop, please feel free to send me a message at stephen.cohen(at)

Thanks.  SC.

Friday, September 11, 2015

This Radiologist Needs to Brush up on her Mechanics

Last week, I injured my shoulder playing soccer; it slammed to the ground after a nasty tackle in my 'friendly' soccer league.  After some nagging from my wife and a few of my students (who got to see what my left hand writes like at the board), I went to get some X-Rays of my right shoulder region taken.

Once in the room with the young radiologist, I was shown where to stand, somewhere between an emitter and receiver of the X-Rays.  She needed to make slight adjustments to my position between exposures.  She would place her hand on my shoulder and/or hip, and push or pull me to the right spot.  And each time it was time to move me, she would state, "Sir, please let me move you."  Eventually, this became, "Sir, please relax and let me move you."  Her frustration seemed to grow as she finally uttered, "Sir, please stop resisting being moved."

I must say, throughout all of this, it took every ounce of my patience to not say: "Enough! I can't take it anymore! Let me explain some basic laws of mechanics to you..."

First off, you cannot push or pull me without being pushed or pulled yourself.  That is Newton's third law, which, if ever violated, would send shock waves through the scientific community.  So, if you expect to push or pull me without getting pushed or pulled back, you must be new at this job.

Second, the extent to which I push back when you push me is related to my inertia or mass.  The amount that you accelerate me from rest with your force has a limit.  It is not a matter of "relaxing my muscles" - the only way you will feel no resistance is if I have no mass.  By saying "Stop resisting being moved," you are essentially telling me to "Stop having mass."  Mass, or inertia, is defined as resistance to linear acceleration.

In the end, I thought it would be smart not to lecture the radiologist about Newton's Laws of Motion.  I held back my urge to scream "Have you never heard of Isaac Newton?"  After all, she was in charge of the amount of high-frequency electromagnetic waves that would be periodically travelling through my body.  She could have responded, "Have you never heard of James Maxwell?"

Wednesday, September 2, 2015

In This House, Mom and Dad Make the Electric Field

In a family with two daughters, aged 3 and 6, the existence of household rules is pretty much a given.  My wife and I are probably lenient compared to many other parents, but maintaining a good environment at home does require some guidelines that the kids come to know.

As I was lecturing about the concept of an electric field yesterday, most of those who were awake were largely unimpressed by the rather abstract concept.  So, here is my attempt to make an analogy so the idea can sink in.

Let us consider my wife and I as "source charges" and our two children as "test charges".  Then, let's label our household rules our "electric field".

The source charges generate the electric field, and the test charges follow them, or go against them, depending on the sign of their charge.  Us parents make the rules, and if one of our daughters is feeling positive, or, agreeable, they follow them.  If she feels confrontational at a given moment, she will surely go against the rules, even if the rule is "eat this chocolate bar" (did I mention I have a 3-year-old?).

Those familiar with the concept of an electric field, realize that in the above analogy, the extent to which a rule is followed or not represents a force.  The relationship between the electrostatic force onto a test charge q in an electric field E is simply: F = qE.  The force onto a test charge within an electric field will either be in the direction of the field or exactly opposite to it.

It is appropriate to equate the electric field to an environment, because that is just what it is.  The rules of the house exist even when a child is not home to obey them or not.  Also, a field has a given direction and magnitude that varies in space.  The rule (direction) in the entrance-way is "take off your shoes when you come in the house," but it is kind of a soft rule that is defied on a daily basis.  "Don't hit your sister!" on the other hand, applies in all spaces and is associated with a large magnitude.  For that reason, when the rule is broken by a negatively charged child, the reaction to it is pretty serious.

A big point of contention in class whenever introducing this concept is "Why don't test charges affect the electric field?"  It is a matter of definition: the source charges establish the electric field - the equivalent to the standard reply "Because we're the parents and we say so."  When the kids grow up, maybe they can become small source charges in the house and have some say on the rules, but not yet.

By definition, an electric field at a given point in space indicates the hypothetical force that would act on a positive charge were it situated there.  Similarly, the rules of the house are made with the presumption that they will be followed by positively charged children.  Right.  My wife and I will need to take a close look at the field we generate, particularly as our little test charges become teenagers.

Monday, August 24, 2015

Locating the Sun Whenever

At around dusk on a recent evening, I came to a logical conclusion while staring up at the half moon in the blue sky.  The Sun was hidden by this time, but I was able to draw a conclusion about its whereabouts.  I just needed to use the Moon as a guide.

First, let vector v1 point from you to the center of the Moon.  Second, let vector v2 point from the center of the Moon to the vertex of the lit up part (as shown below):

Vectors v1 and v2 form a plane.  The center of the Sun lies in that plane.  Think about it.