What is the pulley in a mouse trap car?

The pulley on a mouse trap car acts as an extender (rods balloons etc.) , allowing the force of the pull to be stronger than one without a pulley based on it's positioning. There are 4 ways to use a pulley with a mouse trap car:

1) Leverage
2) Temperance
3) Steering
4) Balance

There are also different types of pulleys to use on a mousetrap car.