Hi, I am in intro physics and have to build an elastic powered car that will be as small as possible, can build quickly and will travel as far as possible. I need a box with all the parts in it. I can use the wheels and axis that are pre-made. After the timer starts timing, I have to re-build my car as fast as possible, setting up the elastic system, and then release the car. Once the car STOPS, the timer will stop timing. The score is calculated using the formula Score = [(volume of box) * (time taken)] / (distance travelled) with the lowest score being the goal. So I think I need a car that can move quickly and stop quickly (since the teacher will continue timing even after I released the car) while travelling a very long distance. I have already spent a day to make a rubber band car, this is how it looks like: Top view: http://www.geocities.com/asdfasdf23135/DSC00707.JPG Bottom view and the wheels: http://www.geocities.com/asdfasdf23135/DSC00708.JPG I used 4 CD wheels, 2 thin axes and a thick rubber band. (I cut the rubber band so it's like a single stretch.) I used tape to stick one end of my thick rubber band on the rear axis and the other end in the front part of my car. It runs quite well on certain surfaces but when I run it on carpet and some smooth surfaces, it is NOT moving, the back wheels are rolling but on the same spot (i.e. not moving). I tried to adjust many different things but I still can't figure out why...and also, I have to roll my car backward for a very long time for it to travel only a short distance. Why? Would a thicker axis improve this? Furthermore, my car is not travelling in a straight line, how can I improve this? Will it get a better performance overall based on the “score formula” if I use: -a wider rubber band? -a long rubber band? -smaller wheels? -larger axis(in diameter)? -2 or more rubber bands? I really appreciate for your help! Thanks a million!