Trial Runs

Today the groups were running some trials to see how close to 20 feet we could get.  It was pretty busy in the classroom and unfortunately I didn't get any pictures or video.  I had two runs that were within an inch of 20 feet.  One run went past, then rolled back and stopped right near the line. 

I was trying to find a way to be consistent with how much I pulled back the car.  The distance the car is pulled back is also the distance that the mass falls pulling the cart forward.

The force from the pull over that distance results in work being done to the cart.  Work results in a change in kinetic energy, which ultimately is a change in speed.  After the car passes under the mass the string no longer pulls on the cart and I rely on friction in the wheels to slow the cart down and stop it. 

My first idea was to use a force probe to determine how much force I was pulling the cart back, but realized that that really didn't help because the force was very similar no matter how much I pulled.  It would have been constant, but the only reason it varied is due to the slight change in angle from the string.

I then marked off how far back I pulled the cart and used that as my variable.  With this approach I was getting much more consistent results.

I'll add some pictures of the design and some data on Monday.

Race-off is Tuesday.  Can't wait!!!