One way to describe a derby car going down a hill is in terms of energy conversion. A car sifting at the top of the hill has potential energy. Potential energy is defined as the amount of stored energy something has that is at some point higher than your reference point. After the ramp paddles are released, the car starts rolling downhill. But that energy has to go somewhere, and most of it is converted into kinetic energy.
Kinetic energy is the energy of motion.
The faster you go, the more kinetic energy you have. It is the driver's implicit goal to convert as much potential energy as possible into kinetic energy. Of course there are other ways we spend energy, so not all of the potential energy is converted into kinetic energy. Other places the energy goes includes the aerodynamic drag acting on the car, particularly at higher speeds, and the rolling resistance of the wheels. Well, it's of course not that simple.