Below is an animation of a rotating disk. Near the edge of the disk is an
(x, y, z) coordinate
system which is, of course, following a curved path. This coordinate system is moving in
circular motion. The
** speed** of the coordinate system is

It is ** accelerating** because its

Since this coordinate system is ** accelerating**,
it is an example of a

Non-inertial frames are accelerating frames.

- The Rotating (X, Y, Z)
- Non-inertial Frame
- Accelerating
- Velocity Is Not Constant

Since this is a non-inertial frame of
reference, you should feel a fictitious force if you are using it as a
reference. And you would. It would be especially noticeable if the
disk were spinning quickly. You would feel pushed
off of the disk. This force is often called the ** centrifugal force**.
It is a

Actually, if you were near the edge of this disk, at any moment your velocity would be
** tangent**
to the circle in which you were moving. In the diagram below you would be
like the blue dot which you could imagine moving in a circle.

Now, pretend this spinning is happening with you on a children's merry-go-round. Almost everyone has been on one of these. At the moment shown above, you are the blue dot, and your velocity is tangent to the circle. According to Newton's first law(which is mostly a restatement of the law of inertia) you should continue to travel in a straight line tangent to the circle. That is, you would try to maintain your velocity and move along the line tangent to the circle as shown in the next diagram:

However, you will want, we will suppose, to stay on the merry-go-round. To do that you will have
to ** 'hang on'** by pulling yourself

Very most likely, however, you will
interpret the pull you provide toward the center as your attempt to resist
somehow being ** 'pushed away'** from the center of the
circle.

The fictitious force away from the center of rotation is called the centrifugal force.

The force you apply, pulling yourself back in toward the center and keeping you on the merry-go-round is called the centripetal force.

Centrifugal force: Fictitious force imagined on an object in a rotating frame of reference. Incorrectly thought as pushing the object away from the center of its circular motion.

Centripetal force: Actual force which must be applied to an object in order to keep it moving in a circle.