Parlor Tricks by Robert Nemiroff Michigan Tech

Physics X: About This Course Officially "Extraordinary Concepts in Physics" Being taught for credit at Michigan Tech o Light on math, heavy on concepts o Anyone anywhere is welcome No textbook required o Wikipedia, web links, and lectures only o Find all the lectures with Google at: "Starship Asterisk" then "Physics X" o

Newton's Cradle A set of balls clacks back and forth showing some kind of physics, but nobody is sure what.

Newton's Cradle Newton's Cradle shows conservation of momentum, conservation of energy, and a shock wave moving through the balls. HOWEVER, the propagating shock wave disallows some clacking variations that also conserve both momentum and energy.

Rattlebacks Can an object spun in one direction stop spinning and then start spinning in the other direction? 1. Yes, that seems OK to me. 2. No, that does not conserve angular momentum. 3. We're sorry, the number you have reached is not in service.

Rattlebacks 1. Yes, that seems OK to me. This occurs for a common type of "stone" called a rattleback. It does not break any physical laws, including conservation of angular momentum. You can order these over the Intertubes (tm). Angular momentum is transferred between the table and the rattleback.

Rattlebacks Below is a YouTube video of a rattleback in action:

Drinking Bird A toy that appears to be a perpetual motion machine. A glass "bird" stands upright for a while, then tips over dipping its beak in a glass of water, then straightens up again. Here is a movie:

Drinking Bird In actuality, the drinking bird is a heat engine. It is not a perpetual motion machine since it would stop as soon as the head stops being cooled by the water. The mechanism is actually pretty complex, but it hinges a liquid that evaporates quickly at (near) room temperature. Since evaporation is a cooling process, and condensation is a heating process, temperatures shift slightly during the birds cycle. The water -- even at room temperature, will cool the bird and add energy to the system.

Dropping a Magnet Through a Charged Disk You have a circular string on which electrically charged balls are affixed all around. You drop a magnet through this string. What happens? 1. The string and balls begin to rotate in one direction, and the magnet rotates in the opposite direction. 2. The string and balls begin to rotate in one direction, but the magnet does not rotate at all. 3. The string and balls begin to rotate in one direction, and the magnet rotates in the same direction. 4. Uncle Tesla calls and asks where you got this idea.

Dropping a Magnet Through a Charged Disk Please don't be upset if you didn't get this right. You might take this opportunity to guess again. Ready?

Dropping a Magnet Through a Charged Disk 2. The string and balls begin to rotate in one direction, but the magnet does not rotate at all. This situation is discussed in Feynman's book "Character of Physical Law" (page 78).

Dropping a Magnet Through a Charged Disk So how does this conserve angular momentum? 1. It doesn't -- this is not a closed system. 2. Considering the charge, the balls themselves actually carry no angular momentum. 3. The electromagnetic field generated carries the opposite angular momentum to the rotating balls. 4. Who cares? Peculiar situations like this are irrelevant.

Dropping a Magnet Through a Charged Disk 3. The electromagnetic field generated carries the opposite angular momentum to the rotating balls. Fields can carry angular momentum.