For my physics EEI i have contructed a gravity car that works by a mass connected by a string and run through pully's to the drive axel. When i drop the mass it pulls the string, spins the wheels and the car propels forward. The car itself weighs approximately 400g The wheels radius on both front and back is 2.25cm The Drive wheels radius is 0.2cm The drop mass falls about 16cm and lands back on the car. I am just a little confused what to investigate in my EEI. I would like to be able to predict it's distance for any given mass on a constant surface and also calculate the co-efficent of friction for the surface using the car. I have plotted displacment/time graphs to find average velocity of the car but thats about it. I'm just not sure where to go from here. I am also trying to investigate torque and angular momentum but i'm finding it difficult. I'm just looking for advice with where to go, and what to do with it.