# I Explanation for this interesting rotational effect?

#### andresB

Summary
An effect that seemingly goes against the law of conservation of angular momentum.
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.

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#### A.T.

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

#### andresB

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?

#### A.T.

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?

#### rcgldr

Homework Helper
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).

#### andresB

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

"Explanation for this interesting rotational effect?"

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