What is a mousetrap powered car and how does it work?

A mouse trap-powered car is powered by the energy of a wound-up mousetrap's spring. The most basic design is to tie one end of a string to the tip of a mousetrap's snapper arm. The other end of the string has a loop that is designed to catch a hook that is glued to a drive axle. Once the loop is placed over the axle hook, the string is wound around the drive axle by turning the wheels in the opposite direction of the vehicle's intended motion. As the string winds around the axle, the snapper's lever arm is pulled closer to the drive axle causing the mousetrap's spring to wind-up and store energy. When the drive wheels are released, the string is pulled off the drive axle by the mousetrap causing the wheels to rotate.

A string is attached to the mousetrap's lever arm and then hooked to the drive axle. The loop knot tied at one end is designed to catch a hook attached to the drive axle. It is also designed so that the string can release itself after the pulling force is spent. If the axle's hook is too long or the string's loop knot is too tight, the string will not properly release from the axle and your vehicle will suddenly stop.

To wind the string around the axle, the wheels are turned in the direction opposite to the motion of the vehicle's travel. It is important that the string NOT be wound loosely or it will snag itself as it is pulled from the axle by the lever arm. Don't push on the mousetrap's lever arm during this process, you want the string to be tight and to pull the lever arm over.

Once the car is released, the string is pulled off the axle and causes the wheels to rotate, which propels the vehicle. If the mousetrap is located too close to the drive axle the wheels will spin at the start and waste energy.

How do you build your mousetrap car?
There's no single way to build one. The best approach is to apply your best understanding of the laws of physics without over exaggerating any one concept to your design. To build the perfect mousetrap car you have to find a balance between all the elements and variable that will affect the car's performance. Be willing to try something original. The first step to making a good car is simple, put something together and find out how it works, it may not be pretty but it's a start. Once you have something working you can begin to isolate the variables that are affecting the performance and learn to adjust to improve your results. Building these cars is a simple process of design engineering, you build, you test and experiment, you change, and you do it all over again.

Considerations
What is the difference between a good speed racer and a good distance traveler?

A good distance car will not be a good speed racer. When you build a car for distance, you want a small energy consumption per second or a small power usage. Smaller power outputs will produce less wasted