The Theory of Relativity Lesson for Kids

Instructor: Elizabeth Foster

Elizabeth has been involved with tutoring since high school and has a B.A. in Classics.

In this lesson, you'll learn about Albert Einstein's theory of relativity, including general relativity and special relativity. Both ideas are very important for scientists who study outer space.

The Theory of Relativity

Have you ever heard of Albert Einstein?

Albert Einstein
Albert Einstein

This guy! He had some pretty crazy hair, but he also had some pretty great ideas.

One of those ideas was the theory of relativity, a scientific explanation about how space relates to time. The theory of relativity sounds very weird and strange when you first hear it. But it's very important for scientists studying outer space and how the universe works.

How Relativity Works

There are actually two theories of relativity, general relativity and special relativity.

Special Relativity

Special relativity says that motion is always relative. Imagine a baseball floating alone in empty space. How do you know if it's moving or not? You can't. But if you put a basketball in space with the baseball, you could see whether the baseball was getting closer to the basketball or further away from it. Then you could see if the baseball was moving.

That's why it's called 'relativity.' The motion of one thing is always relative to the motion of everything else.

Special relativity also says that light always travels at the same speed, 186,000 miles per second. So in one second, light could travel all the way around the planet Earth about seven and a half times!

Now here's the weird part. Special relativity also says that space and time are connected. Time can actually speed up if you're moving slowly through space, or slow down if you're moving quickly. Together, space and time are called space-time. Space-time is like a giant trampoline that can 'bend' around big things like planets and stars.

Special relativity also says that mass, or the total amount of stuff in an object, can change depending on the speed of the object. If you started moving very fast, you would actually have more mass than you do right now.

General Relativity

Now let's go on to general relativity. General relativity explains why things fall towards the ground when you drop them.

General relativity says that space-time is like a big trampoline. Imagine taking a big trampoline, and putting a heavy bowling ball on it. The bowling ball would make a dip in the trampoline and make the trampoline bend down.

The Earth in space-time looks like a bowling ball on a trampoline.
Earth in space

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