Clipped from: The Amazing Rattleback! |
Try to spin it clockwise. Watch it spin, shake, and rattle, and slow down.
Then, watch it spin in the opposite direction!
Clipped from: Sepp Hasslberger: Rattleback 'mystery' explained |
Rattleback 'mystery' explained
A rattleback, also called a celt or wobblestone, is an interesting little piece of material with a roundish bottom and an unbalanced distribution of weight. When spun, it will soon start to rock and then, as the rocking motion subsides, it will settle down to spinning in the reverse direction. Rattlebacks do not work well on a slippery surface, which means that a certain amount of friction is a necessary condition for it to work...
Clipped from: YouTube - russian rattleback |
Clipped from: Rattleback - Wikipedia, the free encyclopedia |
Physics
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.
This explains why, due to friction, most rattlebacks exhibit spin-reversal motion only when spun in the pitching-unstable direction, while they slow down and stop spinning before the rolling instability arises when spun in the "stable" direction. Also, after stopping, the spin in the "stable" direction is considerably slower than the original spin speed. Some rattlebacks, however, exhibit "unstable behavior" when spun in either direction, and incur several successive spin reversals per spin.[3]
Other ways to add motion to a rattleback include tapping by pressing down momentarily on either of its ends, and rocking by pressing down repeatedly on either of its ends.
Clipped from: YouTube - Rattleback |
Clipped from: YouTube - Rattleback slow motion |
Rattleback slow motion
Clipped from: YouTube - celt, rattleback, wobblestone |
Sources:
- The Amazing Rattleback!
- Sepp Hasslberger: Rattleback 'mystery' explained
- YouTube - russian rattleback
- Rattleback - Wikipedia, the free encyclopedia
- File:Rolling-pitching.png - Wikipedia, the free encyclopedia
- YouTube - Rattleback
- YouTube - Rattleback slow motion
- YouTube - celt, rattleback, wobblestone