Difference between rotation and revolution

Rotation is the motion of planets, hands of clocks, gears, blades of helicopters, and an ice skater.

At some point in your life, you may have heard of the earth's rotation and revolution. However, there is a difference between rotation and revolution although many people think that these two terms mean the same.

If the difference between these two types of rotational motion is not crystal clear to you, this lesson will make it clear.

The rotation we will discuss here usually happens with a rigid boby and a fixed axis. A rigid body means that all the body's parts are locked together and its shape will not change. For example, the sun is not a rigid body since the sun is a big ball of gas that is not locked together. 

An example of an axis that is not fixed is the axis of a moving bowling ball. While the bowling ball rotates about an axis, the axis is not fixed since the axis moves with the ball.

Now here is the difference between rotation and revolution. When the fixed axis is located within the rigid body, the motion is called rotation.

However, when the rigid body turns about an external axis, the motion is called revolution.

The platform of a carousel rotates about an axis. However, the correct thing to say for the children or parents seating on the horses is that they revolve about the axis. For the parents and the children the axis of the carousel is an external axis. However, for the carousel, it is an internal axis.

Try the following experiment.

Get a paper plate and put a piece of chicken anywhere except at the center. Put your index finger at the center of the paper plate. Use the other hand to rotate the paper plate.

The plate is a rigid body and your finger is now a fixed axis for the plate.

You can say that the plate rotates about your finger. However, the piece of chicken on the plate revolves about your finger.

It is quite possible for an object to experience both types of rotational motion. If you get yourself on a platform that is rotating and you spin your body at the same time just like an ice skater, then you are revolving and rotating at the same time.

The earth is a great example of rotation and revolution happening at the same time. The earth rotates around an imaginary axis that passes through the north and south poles of the earth. It takes the sun about 24 hours to complete 1 rotation. 

Furthermore, the earth revolves around the sun. It takes the sun 365 and 1/4 days to complete 1 revolution.

By now, hopefully the difference between ratation and revolution is clear in your mind.

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