A key part to understanding motion is being able to describe it.

Motion where? How fast? Which way?

One way we do this is by using distance. It’s the space between two objects or points. It could be centimeters or lightyears!

It all depends on the size and what measurement makes the most sense. The farther away something is, the bigger the measurement you can use.

When this gets tricky is when your reference point is something super big, like the moon!

That’s why it always looks like the moon is following you when you’re riding in a car even if you’re moving at a high speed!

Speaking of speed, what is it?

Speed is distance over time, or how far you travel in a certain amount of time!

Think about speed limit signs on the road.

This one in our imagination says 30 mph, or 30 miles per hour. If you’re listening to the sign, your speed means you will travel 30 miles in one hour.

Just like distance, you can measure speed in different ways too! It depends on how fast something is moving and how far it is going, or what makes the most sense for you in the moment. Inches per hour might make sense for a snail. Meters per second is often used in science!

Any change over time is called a rate. Speed is a rate!

The thing about speed is that you rarely go from one place to another at the same rate. You might speed up from 20 mph to 30 mph, slow down to 5 mph, or even stop completely.

When you’re on a bike, your speed changes almost constantly.

In that case, you can find the average speed. That would be the total distance traveled over the total amount of time.

Velocity

Maybe you’ve heard the word velocity before. Sometimes people think velocity is the same thing as speed, but it isn’t.

Imagine you’re watching the tv when suddenly there’s breaking news. The weather person says there is a tornado located in your town moving at 50 mph. 

Are you safe? How do you know?

Speed alone doesn’t tell us much. We need more information, like directions!

North, South, East, West, Weast, Up, Down, Left, Right.

Direction!

Velocity is speed plus direction

What this means though is that even if something has a constant speed, its velocity might change.

Think about cars at a racetrack. They’re driving in circles. Every time their direction changes, their velocity changes.

It’s also possible for two objects to be moving at the same speed, but different velocities.

Two elevators, one moving up and one moving down, two basketball players heading straight towards each other on the court. Same speed, different Velocity!

Most of the time, when we think about motion, we are thinking about something moving fast, but motion can be incredibly slow too. Think about it. We can use slow motion cameras to watch fast things happen slowly, or time lapses to watch slow things happen quickly, like a tree growing, or an egg growing into a tadpole. 

Motion is any movement, no matter how fast or how slow.

Even glass moves over time. The whole planet moves! Continents first closer together and farther apart. Earth moves one full circle around the sun every year. The whole universe is in motion!

It’s all just a matter of your perspective.

But your perspective might change depending on your own motion. This idea is known as relativity. When you’re biking next to a friend, they look like they are moving at normal speed, but if you are standing and they ride past you, they look like they’re moving way faster, even if their actual speed is the same. 

Astronauts in the space station look like they are moving slowly and weightless, but they are actually falling around the earth at speeds of nearly 5 miles per second. Everything just looks slow because it’s all falling at the same speed. 

When you’re in a car with your family, you might be moving at 70 mph, but it looks like everyone is moving normally. 

 Speed looks different depending on your own speed.