Why is it unfair if one car starts higher on the ramp?

Have you ever raced toy cars down a ramp made from a big book or a board? Listen to the wheels whirr as they roll down and zoom across the floor. Now picture your friend setting one car higher up the ramp than yours.

Right away, you can feel that something is wrong with that race. So why is it unfair if one car starts higher on the ramp? Let's find out together.

First, think about why a car rolls down a ramp at all. You let go, and an invisible pull tugs it downward. That pull is called gravity, which means the pull that brings things down toward the ground. Gravity is the same pull that makes a dropped spoon land on the floor.

As the car rolls, gravity keeps tugging on it the whole way down. With every bit of ramp, the car speeds up a little more. It stops speeding up only when it reaches the flat floor.

Now picture two cars on the same ramp. The red car sits at the very top, and the blue car sits halfway down. That means the red car has a much bigger drop ahead of it. Which car do you think will be zooming faster when it reaches the floor?

The red car is zooming faster! Gravity tugged it down a bigger drop, so it had more ramp to speed up on. It shoots off the end and rolls much farther across the floor.

Here is the unfair part. The red car won, but is it really the better car? Nobody can tell, because it started higher. The race only showed which car got the higher spot, not which car rolls best.

To make the race fair, everything has to be the same except the one thing you want to check. In this race, you want to check the cars. So both cars need the same ramp and the same starting spot.

Line both cars up side by side at the very top, and let go at the same moment without a push, so only gravity gets them moving. Now gravity pulls both cars down the same drop. In this fair race, if one car rolls farther, the car itself made the difference.

So our key word is gravity. Gravity pulls a car that starts higher down a bigger drop, so it goes faster because of where it starts, not because it is a better car.

Sleep well, little racer, and may every race you set up be a fair one.