Mousetrap Car Paper


Physics 2


5/26/04


Mousetrap Car Paper


Intro


First off, all calculations are shown on the attached page. Please don’t judge how I did the distance calculations and some leading up to them, I used those solely for my own purpose and understanding in hopes that I could make a spreadsheet to find the best distance to speed ratio for total distance.


A Few Things Found Along the Way


I started off with a car that was about 1.3 meters in length. I put the mousetrap fairly close to the rear axel and made about a half meter lever arm that stuck out the back further than the rear axel. I used the bottoms of buckets for my rear wheels and some small ones in front. It hit an 8-9 m mark right off the bat. It went pretty fast so I extended the lever arm. I kept getting the same results over and over even after extending the arm to 3 m or so. I changed the rear wheels to 12” records and they dramatically improved my results. I found out later, though, why increasing the lever arm did nothing to change my results (this was just Tuesday, the night before this paper was due). I found that after the lever arm is past the rear axel, the amount of string wound up is only about twice the distance between the axel and the spring. So I figured I had a lot of extra weight and pretty much started all over.


Now


Now I have a much better and shorter car with the same rear wheels and a much shorter lever arm, greatly decreasing the weight of the car and therefore the force of friction. After playing around some, I found that it was best to put the spring 10-15 cm from the rear axel and to make the arm a little bit longer than that distance. I use a very small axel and a large wheel because I get a much greater distance at the sacrifice of force do to the wheel to axel ratio and the basic physics of simple machines. My wheel to axel ratio is about 30:1. I also used records for my wheels not only because they’re big, but because they’re thin, decreasing their weight as well as the surface area for friction, which is why I also changed the front wheels to CD’s, they are much thinner than my previous wheels, allowing a longer coasting distance. All I’ve really done to fix my car is use graphite to decrease the coefficient of friction at the axel. I also drilled a few holes in my car to make it lighter, both of which decrease the force of friction. So far I’ve gotten the overall coefficient of friction down to about 0.19 and the force of friction to -0.75 N. My car weighs about 0.4 kg and accelerates at 0.2 m/s2. It should go close to 9 meters just by the pull of the string and then coast the rest of the way. I’m not very sure if it actually goes that far yet because I run into carpet and my car stops because the carpet has a much greater coefficient of friction than the linoleum in my kitchen. And that’s about it. Everything else is on the calculations page.