# Rolling and translation motion

• Gyroscope
In summary, the conversation discusses the effects of friction on a ball's motion on a flat surface. It is noted that friction can slow down translational motion while increasing rotational motion. However, the question arises as to why the ball does not continue to roll when it stops moving. After rephrasing the question, it is clarified that if the ball has both rotational and translational motion, friction will cause it to roll without slipping. However, if the ball starts with pure rotation, friction will speed up the translation and slow down the rotation until it rolls without slipping in the opposite direction.

## Homework Statement

I throw a ball rolling and moving through the a flat surface. I may say that friction is slowing down translation motion, but increasing rotational motion, so when the ball stops moving, why is it not rolling? That's confusing me a bit. What can you say?

Last edited by a moderator:
Can you rephrase your question. If the ball is at rest (no translational motion or acceleration) how can it be rotating with friction present? (Is that what you mean by rolling?)

I am sorry, my english did not let express as well as I would like to. The ball initially has rotational and translational motion.

OK. If the ball starts with a motion such that the speed of its bottom surface (with respect to the floor) is anything other than zero, then kinetic friction will be exerted on the ball in a direction that opposes the slipping between the surfaces.

For example: If the ball starts out in pure translation, then friction will slow the translation and speed up the rotation--up until the point that the ball rolls without slipping.

And if the ball starts out with pure rotation?

Thanks again for helping me.

Gyroscope said:
And if the ball starts out with pure rotation?
The direction of rotation will determine which way friction will act and the direction that it will roll. This time kinetic friction will speed up the translation and slow down the rotation until the ball rolls without slipping.

## 1. What is the difference between rolling and translation motion?

Rolling motion is a combination of rotational and translational motion, where an object both rotates and moves along a surface. Translation motion, on the other hand, is a straight-line motion with no rotation.

## 2. What factors affect the rolling motion of an object?

The factors that affect rolling motion include the shape and size of the object, the surface it is rolling on, and any external forces acting upon it.

## 3. Can an object have both rolling and translation motion at the same time?

Yes, an object can have both rolling and translation motion simultaneously if it is rolling on a surface while also moving in a straight line. This is commonly seen in objects such as wheels or balls.

## 4. How does friction affect rolling motion?

Friction plays a crucial role in the rolling motion of an object. It creates a force that opposes the motion of the object, causing it to slow down. However, it also provides the necessary traction for the object to roll without slipping.

## 5. Can the speed of an object in rolling motion be constant?

Yes, the speed of an object in rolling motion can be constant if there is no external force acting upon it. In this case, the object will continue to roll at a constant velocity without accelerating or decelerating.

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