How to Win a Hot Wheels Derby on a Moving Treadmill

Hot wheels on a treadmill ? Why didn’t anyone think of this sooner? As you can see in the video, this guy put a whole bunch of toy cars on an incline treadmill. After that, he just slowly increased the speed of the track. There you have it: an instant demolition derby. It’s kind of fun to watch cars collide and then be thrown off the back of the conveyor belt.

But of course there are questions here, questions of physics. I will answer it for you.

Why are some cars faster than others?

Imagine that these cars are just blocks on a low-friction inclined plane. (It’s easier that way.) With this I can show the forces acting on each car (block).

Illustration: Rhett Allain

We have three forces. First there is the gravitational force that pulls down. It depends on both the mass of the object (m) and the gravitational field (g = 9.8 Newtons/kilogram). It is easy strength.

The next is FNOT. This is normal strength. It is an interaction between the car and the surface. The purpose of this force is to prevent the car from moving through the surface. It is a constraining force, that is, it has just the right value to keep the block on the inclined plane.

Finally, there is the kinetic frictional force (FK). This force depends on two things: the magnitude of the normal force and a defined coefficient of friction for the two interacting materials. For the current Hot Wheels car, the kinetic friction is not between the wheels and the track, but rather between the wheels and the axles.

As an equation, the kinetic frictional force can be modeled as follows:

Illustration: Rhett Allain