What Causes the Vibrations in a Spinning Toroid?

[Prannoy Mehta]

In our class we were playing with a toroid shaped object made of foam (Probably). While tossing it around, not only was the disc rotating simply. It was well, sort of vibrating. Like one end of the object is up and the other is down then after a small interval the vice versa occurs. What is the main cause of this phenomena ? Is this an example of a toroid shaped example.

Thank you.

 

[Khashishi]

You mean like the handle shown here?

This is a consequence of the intermediate axis theorem. https://en.wikipedia.org/wiki/Tennis_racket_theorem
also explained here:

 

[Hornbein]

In our class we were playing with a toroid shaped object made of foam (Probably). While tossing it around, not only was the disc rotating simply. It was well, sort of vibrating. Like one end of the object is up and the other is down then after a small interval the vice versa occurs. What is the main cause of this phenomena ? Is this an example of a toroid shaped example.

Thank you.

I have a personal theorem: if it can vibrate in some way, then it will.

 

[Prannoy Mehta]

No, the intermediate axis is supposed to be stable. The axis we rotated passes about the centre, and is the axis passing vertically, when the donut is kept flat on the floor like this http://38.media.tumblr.com/38ac875dcfe9254f0fde171aa14cf211/tumblr_n6rat2uMwq1r8bo1oo1_400.gif

But at much much higher speeds.. This axis seems to be very stable..

 

[Khashishi]

I think we need more detail on what you observed. How long was this torus in the air? How dense is this foam? Could air resistance be a factor? How symmetric is the shape?

 

[Prannoy Mehta]

It was symmetric, there were no visible signs of damage. Torus was in the air for perhaps maximum 1-2 seconds, we were throwing it from one end of the class to the other The distance it traveled was about 10 - 15m. Density of the foam is something I can't comment but it was as squishy as a tennis ball. Can't comment about air resistance. It was non porous, and did not seem to be hollow.

 

[Khashishi]

I'd say distance traveled was too short to make any clear conclusion without sophisticated equipment.

 

[Prannoy Mehta]

I will try at larger distances tomorrow when we go back to school.. Thank you :)

 

[Prannoy Mehta]

Here is the video:

https://onedrive.live.com/?id=554BC...AAF8931B!190&authkey=!ACOb8EwyVup1Tj8&o=OneUp

Hope the poor lighting does not make a big difference..

 

[Prannoy Mehta]

Hello Anyone ? Please reply ?

 

[Khashishi]

Seeing the video, there's nothing strange going on at all. When thrown, the angular momentum is not aligned with the major axis. This is because the thrower isn't perfectly spinning the torus along this axis.

 

[Prannoy Mehta]

We tried, doing many other experiments with this. First one was, throwing it diagonally because I assumed that could be a good answer, it din't work. The torus spun perfectly no vibrations at all. Then we suspected something to do with the velocity inside and outside (Air resistance) We covered it with foil on one side, the vibration increased, when covered on both sides there were no vibrations. Then we threw it vertically, vibrations occurred. The video of the other cases has been misplaced. The foil seemed really convincing but we failed to come up with appropriate reasons to why it would go up and down.