# Explanation for this interesting rotational effect?

• andresB
In summary, the video shows an effect around minute 1:20 where the un-twist of the elastic band and the rotation of the ball about the line joining them keeps the initial zero angular momentum constant. This may be similar to the Dzhanibekov effect, although not directly related. The conversation also discusses the conservation of angular momentum in a non-isolated system, with one person questioning why it should be conserved and another pointing out that the reverse rotations are caused by the interaction of the balls with the table. The conversation also touches on the concept of a closed system and how the surface and the Earth would need to be included in order for it to be truly isolated. Additionally, the question of how the balls start moving
andresB
You can see the effect around minute 1:20 in this video. It seems to me that the un-twist of the elastic band and the rotation of the ball about the line that joins them is what keep the constant the initial zero angular momentum, though I can't tell for sure.

The inversion of in the direction of rotation somewhat reminds me of Dzhanibekov effect, though most likely not related at all.

andresB said:
An effect that seemingly goes against the law of conservation of angular momentum.
Why should angular momentum be conserved in a non-isolated system?

FactChecker
A.T. said:
Why should angular momentum be conserved in a non-isolated system?

Are you saying that the reverse of the rotations comes from the interaction of the balls with the table?

andresB said:
Are you saying that the reverse of the rotations comes from the interaction of the balls with the table?
Why just the reverse? How do you think the balls start moving in the first place, after being released?

A.T. said:
Why should angular momentum be conserved in a non-isolated system?
To clarify A. T.'s post, the balls exert a torque onto the surface, so to be a closed system, you'd have to include the surface and whatever the surface is attached to (like the earth).

A.T. said:
Why just the reverse? How do you think the balls start moving in the first place, after being released?
That makes sense.

## 1. What is the cause of this rotational effect?

The rotational effect is caused by the conservation of angular momentum. When an object is set into rotation, it will continue to rotate at a constant speed unless acted upon by an external force.

## 2. How does this rotational effect occur?

This effect occurs due to the distribution of mass and the distance from the axis of rotation. Objects with a larger mass and/or a greater distance from the axis of rotation will have a greater rotational effect.

## 3. Can this rotational effect be seen in other systems besides objects in motion?

Yes, the conservation of angular momentum applies to all systems, not just objects in motion. For example, it can be observed in the rotation of planets around the sun or in the spinning of a top.

## 4. Is there a mathematical formula for calculating this rotational effect?

Yes, the formula for angular momentum is L = Iω, where L is the angular momentum, I is the moment of inertia, and ω is the angular velocity.

## 5. How is this rotational effect used in everyday life?

This effect is used in many everyday objects, such as bicycles, cars, and even in sports like figure skating. It is also used in technologies like gyroscopes, which are used in navigation systems and stabilizers for cameras and drones.

• Other Physics Topics
Replies
39
Views
932
• Mechanics
Replies
13
Views
2K
• Mechanics
Replies
6
Views
2K
• Mechanics
Replies
8
Views
5K
• Mechanics
Replies
14
Views
2K
• New Member Introductions
Replies
2
Views
40
• Mechanics
Replies
12
Views
3K
• Mechanics
Replies
12
Views
5K