Perpendicular

Let's pretend that you have a toy car and you want to measure how straight the wheels are. One way to do this is by placing a long stick or ruler next to the wheels.

If the stick is touching both wheels at the same time and is perfectly straight up and down, that means the wheels are going in the same direction and are parallel to each other.

But, what if you turn one of the wheels to the side a little bit? When you place the stick next to the wheels, it will no longer touch both wheels at the same time. Instead, the stick will touch one wheel on one side and the other wheel on the other side.

This means the wheels are no longer parallel and instead they are perpendicular to each other. The word "perpendicular" means that two things meet or cross each other at a 90 degree angle, just like how the stick is touching both wheels at a 90 degree angle.

So, next time you see two things that meet at a right angle, you can say they are perpendicular!