Well, we have a Physics project which requires us to build a car and power this using energy provided by a mousetrap. We may not add other energy sources to power the car; we can only use the mousetrap provided to power the car. 2. Relevant equations Now, thinking about strings and energy transfer, I thought that maybe by taping string to the snappy end of the mousetrap, and then tying the other end to the axle, which is attached to the wheels, I could transfer energy from the mousetrap to the wheels. However, I'm worried about the string bundling or curling up when the axle spins to power the wheels. What should I do?