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### Circular Motion and Acceleration

```
Date: 12/03/1999 at 05:07:52
Subject: Circular motion

How can an object experiencing circular motion always be accelerating
toward the center if the distance from the center is constant?
```

```
Date: 12/03/1999 at 13:04:01
From: Doctor Rick
Subject: Re: Circular motion

Hi, Ben.

Circular motion is confusing, I know. We must distinguish "circular"
concepts from "linear" concepts. If an object maintains constant
distance from the center, we say that it has zero "radial velocity"
constant. These are "circular concepts." But the object still has
non-zero "linear acceleration," which we just call acceleration.

Acceleration (linear acceleration) means deviation from constant
velocity. Constant velocity means motion at constant speed in a
constant direction. An object in circular motion is constantly
changing direction, and thus it is accelerating. The direction of this
change in motion (acceleration) is toward the center.

If the object stops accelerating - if, for instance, you were swinging
it on a string and the string were to break - it would move in a
straight line tangent to the circle. Its distance from the center (or
what had been the center) would increase.

If you compare the motion of the object in circular motion with this
tangent-line motion of an unaccelerated object, you will see that the
circular motion causes it to be closer to the center than it would
have been if it were not accelerated. Thus, it is accelerating "toward
the center."

- Doctor Rick, The Math Forum
http://mathforum.org/dr.math/
```
Associated Topics:
High School Physics/Chemistry

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