# Angular Acceleration: Motion, Force & Direction

• MHR-Love
In summary, when you rotate the rod and collar, the rod and collar both move away from the center of rotation. This is because the rod and collar have a radial force that is directed toward the center of rotation.
MHR-Love
Hi guys,
supposing there is a collar which can freely move along a rod. If the rod is rotating with a certain angular velocity, the rod will move away from the rotating point (it can never move towards the point). The acceleration of the collar has a radial component toward the point, hence the radial force acting on the collar has a direction toward the rotating point.
My question is why are their directions towards the point while the motion of the collar is out??
when I pull a box, the box's acceleration will have the same direction as the my pulling force and so does its motion. What makes the collar analysis different?
Thnx

The two scenarios you mentioned are not different. They are the same. When you pull on the box, the box exerts a reaction force in the opposite direction, pulling back on you. Likewise, when you rotate the rod and collar, you are pulling on them toward the center point of rotation; and the rod and collar exert a reaction force in the opposite direction, pulling away from the center of rotation.

If you stop pulling on the box or the rod and collar, all of these objects will continue moving in a straight line, unless other forces change or stop them. Therefore, the box keeps moving toward you, and the rod and collar keep moving perpendicular to you, which is away from you.

Last edited:
nvn said:
The two scenarios you mentioned are not different. They are the same. When you pull on the box, the box exerts a reaction force in the opposite direction, pulling back on you. Likewise, when you rotate the rod and collar, you are pulling on them toward the center point of rotation; and the rod and collar exert a reaction force in the opposite direction, pulling away from the center of rotation.

If you stop pulling on the box or the rod and collar, all of these objects will continue moving in a straight line, unless other forces change or stop them. Therefore, the box keeps moving toward you, and the rod and collar keep moving perpendicular to you, which is away from you.

Thnx for replying, I thought of your answer by imagining that I am rotating a ball of mass m using a string attached to it, so I feel like my hand is pushed away because of this reaction. Thnx and happy day

## 1. What is Angular Acceleration?

Angular acceleration is a measure of the rate of change of angular velocity over time. It is a measure of how quickly an object's rotational speed is changing.

## 2. How is Angular Acceleration calculated?

Angular acceleration is calculated by dividing the change in angular velocity by the change in time. The unit of angular acceleration is radians per second squared (rad/s²).

## 3. What factors affect Angular Acceleration?

The factors that affect angular acceleration include the magnitude and direction of the applied force, the mass and distribution of mass of the object, and the distance from the axis of rotation.

## 4. How is Angular Acceleration related to Force?

Angular acceleration is directly proportional to the torque or rotational force applied to an object. This means that the greater the torque, the greater the angular acceleration.

## 5. Can Angular Acceleration be negative?

Yes, angular acceleration can be negative. This indicates that the object is slowing down in its rotational motion or changing direction in a clockwise direction.

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