Plastic thing that will spin only one way? Wtf?

[Joza]

Plastic thing that will spin only one way!? Wtf?

Has anyone a clue how this works?

In the video, the guy demonstrates a piece of plastic that will spin only one way. Just look at the video, you will see what I mean. It's really impressive, and I must know how it works!

It's at about 4 minutes into the video.

Link deleted: Ivan

 

[Doc Al]

The Amazing Rattleback!

That toy is called a rattleback--they've been around forever. Pretty cool, eh? The physics is complicated. Check this out for a taste: http://www.4physics.com:8080/phy_demo/rattleback.htm"

By the way, that video is full of wild crackpottery and nonsense. Don't waste your time with it.

 

[Ivan Seeking]

That is called a rattleback and it is well understood.
http://physicscourses.okstate.edu/ackerson/museum/Rattleback.htm

The link in the op has been deleted since the material within violates the posting guidelines.

Edit: Whoa! Doc Al is fast on the keys today.

 

[rocomath]

damn that was tite, i love scienceee!

 

[Joza]

Well that was cool!

Indeed, apologies for the link. I am interested in the study of UFOs, and came across the video but I have lost respect for David Sereda now. I admired his study on UFOs before, but he was so amazed and taken back by such known physics (even the induction one) , and he supposedly has a degree in physics.

 

[Ivan Seeking]

Well that was cool!

Indeed, apologies for the link. I am interested in the study of UFOs, and came across the video but I have lost respect for David Sereda now. I admired his study on UFOs before, but he was so amazed and taken back by such known physics (even the induction one) , and he supposedly has a degree in physics.

That's okay. We do discuss specific UFO events. and we consider the evidence - anecdotal and otherwise - for those events, but we don't get into exotic theories [ET] in order to explain them. We all know that many people claim that ET is here, but without proof of this claim, that's about as far as we go on that point - we recognize that the claim exists. The Hutchison stuff is a banned topic altogether. The rest of what I heard on that link was nonsense as well.

I've been following the UFO enigma for over two decades. I'll let you know when I know what to think of it all. However the rattleback is explained, and it doesn't require nuclear physics as was seemingly suggested in the video.

 

[J77]

If you're interested in cool geometries -- tho with rocking, not spinning -- check this out: http://www.gomboc.eu/

 

[mgb_phys]

That is called a rattleback and it is well understood.

Not by me or most students I've shown it to

 

[michealsmith]

Yeah , its a classical physics toy ...ask in the classical physics section they'll tell you.

 

[DaveC426913]

Not by me or most students I've shown it to

I saw this just the other day. The curve that it rocks on is not symmetical; it is slightly more curved in one direction than the other. Momentum is conserved in both directions of rotation, but the period of the rocking, while smooth in one direction, sets up a destructive rocking in the other direction (sort of like what happens before you get a skipping rope up to speed).

From Wiki:

The spin-reversal motion follows from the growth of instabilities on the other rotation axes, that are rolling (on the main axis) and pitching (on the crosswise axis).

When there is an asymmetry in the mass distribution with respect to the plane formed by the pitching and the vertical axes, a coupling of these two instabilities arises; one can imagine how the asymmetry in mass will deviate the rattleback when pitching, which will create some rolling.

The amplified mode will differ depending on the spin direction, which explains the rattleback asymmetrical behavior. Depending on whether it is rather a pitching or rolling instability that dominates, the growth rate will be very high or quite low.

 

[mgb_phys]

I know (on paper) how it works - it was the statement that it was 'well understood' that was slightly ironic.

A bit like Hardy allegedly stopping in the middle of a proof in a lecture, doing 2 hours of frantic calculation, and continuing with "yes, it is obvious that..."

 

[K.J.Healey]

So this thing would pretty much spin normally on a frictionless surface, right?

 

[Ivan Seeking]

Yes. This is from the link that I posted.

Fig. 3 When the Rattleback shown above rocks from side to side, its skew symmetry makes it rock along the diagonal line. When it rocks to the left, the contact point is above the horizontal line and the object center of mass tends to fall downward relative to the contact point. Friction thus acts downward to prevent slipping at the contact point. When the Rattleback rocks to the right, the contact point is below the horizontal line and the object center of mass tends to fall upward relative to the contact point. Friction thus acts upward to prevent slipping at the contact point. The forces acting on either side of the center of mass tend to produce a counterclockwise rotation