Hotwheels Friction Sled

This is a sled designed to be placed at the end of a section of hotwheels track. The car rolls into the sled and then slides across the desk/floor. In my classroom I use this as part of our Work and Energy unit. I set up the track like a ramp do the car rolls down and into the sled. Students calculate the gravitational potential energy of the car at the top and measure the distance the sled slides. With this students can use conservation of energy to determine the work done by friction on the sled, then using the distance the sled slid they can find the force of friction on the sled, and even the coefficient of friction.