Understanding Motion: Centripetal & Projectile Motion

Here’s where motion starts a commotion. Remember how something can travel at a constant speed but have a change in velocity? 

Let’s think back to those race cars, or even a carousel. The cars or animals are moving at a constant speed, but because their direction changes constantly since they are moving in a circle, that means they are accelerating. In both of these cases, the direction of acceleration goes towards the middle.

This is called centripital motion. Think about the Earth. The earth moves at a constant speed around the sun but its velocity is always changing. That puts the direction of acceleration straight towards the sun, so we stay in orbit around the sun!

There’s one last type of motion we’ll learn about today. That’s projectile motion. 

When you throw a ball to someone, especially if they are farther away, you have probably noticed the ball doesn’t just travel straight. It starts to fall lower towards the ground. To throw something farther, you have to throw it at a higher angle. This is because earths gravity is constantly trying to pull everything toward it. Rubber bands, balls, bullets, and boomerangs all have to deal with projectile motion. Anything shot or thrown will eventually curve down to the ground. 

What’s weird though is that no matter how fast or how hard you throw or shoot an object, if you drop the same object from the same height, they will hit the ground at the same time.

Try it with two tennis balls and a timer, or look up the Mythbusters bullet experiment on YoutTube. 

A dropped ball and a thrown ball both have gravity pulling them towards the ground at the same rate. The thrown ball just travels greater overall distance to reach the ground.

It’s like this. Imagine you drop a baseball on the ground. Okay, gravity acted on the ball to bring it to the ground. Now imagine you’ve thrown the ball. It’s moving faster than the one you dropped, but all that speed  just helps it move farther out away from you before hitting the ground. 

That’s all for today. Next time, we talk Forces and Newton’s Laws.