By definition, angular acceleration is the change in velocity during a rotation per unit of time.

### Angular Acceleration Explained

The best way to understand angular acceleration is to break it down to the basics. It starts with an understanding of position and builds up to concepts like speed and **angular velocity**.

#### 1) Position

If you start small and think about a resting toy car, it stays in one place. There's no speeding up or slowing down.

The only way it'd move is if it was pushed hard enough. And if that happens, the car's position changes.

Sure, you could see how big the distance between the two positions is. But, how would you know how fast the toy car was going?

### 2) Speed

Speed isn't just about distance. You could measure how far something rolled, but that doesn't answer how quickly it went.

It's the factor of time that creates speed.

##### Example

Let's say the toy car turns out to have gone 4 feet in 2 seconds. What's the speed?

We might be tempted to convert that into **mph**, but it's good the way it is.

#### 3) Velocity

Sometimes it's not enough to know how fast something is going alone. It's important to factor in the direction something is traveling in.

Turns out velocity is as simple as this. It's speed with the concept of "direction" factored into it.

##### Example

Consider a drag car with a parachute. It's definitely going in one direction, but when the parachute releases, there's a force acting upon it in the opposite direction.

So it's useful not only to know how strong forces are but also where they're pointing to.

#### 4) Acceleration

If you think about it, the original speed question is really asking, "At what rate is our position changing?" Velocity is how quickly that particular change happened.

But, for better or for worse, the world is more complicated than this. If there were only velocity, how would anything start moving in the first place?

That is, if a car only ever moves at a constant rate (e.g., 70 mph or 2 ft/sec) or not at all, then how is it that NASCARs and airplanes don't go on moving forever?

When they start up their engines, they don't go full speed right off the bat. It's a slow curve upward.

This is because there's a rate of change for not only position, but also velocity itself.

And acceleration is the rate of change of velocity, or, "How fast is something speeding up or slowing down?"

#### 5) Angular Velocity

Now, think about when a race car turns. Its entire body is shifting at an angle.

It was at one angle coming into the turn, and went to another angle coming out of it. The distance is the angle of change.

There was an average speed at which that all happened, called angular velocity.

#### 6) Angular Acceleration

While that race car is turning, it's speed varies throughout the turn.

Initially, its momentum is big and positive, but as the turn comes to an end the car's acceleration will die down as it's no longer needed.

This is the essence of angular acceleration. It's the rate of change in angular velocity, or, "How fast is something speeding up or slowing down during a change of rotation?"