Coin Science: What happens to coins over time?

    A new company (Coinweigh, Inc.) is trying to secure a patent for a device to revolutionize the vending machine world. Current methods for vending machines to determine which coin you dropped are mechanical or optical in nature. Both have their downsides in that counterfeit coins get through. Coinweigh, Inc. wants to market a mechanism that measures only the mass of the coin. Based on that data alone, it decides what denomination coin has been inserted.

    The engineers need to know what tolerance to put on the mass measuring device. They need to know if the coins will change mass over time, and you are going to expalin to them if it does (or not) with data to back it up.

    They have contracted your company (lab section) to determine what the if coin masses change significantly over time, and if so, but what %. You have also been asked to comment on the procedure and make recommendations on any new methods you think might be more effective.
Your report (15 points total) consists of the following pieces:
Procedure: A short 3-5 sentences description of what the class did. Short and sweet, but be complete, including what calculations you did and what the other groups did. The reader should be able to 'reproduce' your data using just your procedure.
Results: Put in your numbers as well as the class numbers, well labeled with some words to make it understandable.
Conclusions: Here is where you include the conclusions made by the class after all the data was crunched.
Sample Calculation: You need to show the long drawn out (hand-written is OK) method for calcualting standard deviation. It need to look professional, so don't include your not-very clean work you did in lab.

   You have exactly three hours to discuss the problem and collect all the data that you need. You will have one week to compile the data and write your report. Computers will be around for your use, but each group must compile and process their teams data. All team data will be collected near the end of the period such that everyone has the entire class's data. At the beginning of class you will be given the opportunity to discuss the situation with the senior technician who will be receiving the reports. His purpose is to answer your question regarding the experiment, so make sure you have some. His is a nice guy, but is not going to tell you what to do.

   You will be supplied with a large number of one kind of coin (all with dates of manufacture) your team will be 2-3 people as assigned by your instructor. Balances will be made available to you as well.

Before lab, you must be familiar with how to calculate averages and standard deviations (SD). Standard deviation is defined as 

Here is one site with a nice description what SD is and (at the bottom) how to calculate it. Another 


1. What is the average and standard deviation of the following data set: 3.4 cm, 3.7 cm, 3.2 cm, 3.9 cm, 3.1 cm, 3.4cm ? Show your work and be detailed in showing your method. Do NOT simply put the data in your calculator and give me the final result.

2. As a coins gets 'older' what do you expect to happen to the mass of the coin? There is no right/wrong answer. Defend/explain your answer.

3. Pretend for a moment you are the supervisor for all the other scientists in lab Give a short (3-5 sentence) plan of action for the day to be given to your scientists.

~MEO 9.13.07