Gyrotwister

A Gyrotwister consists of a wheel that can spin at several thousand rounds per minute, that is rigged up inside a semi-transparent ball so that it can also move around a horizontal axis, in much the same way that the earth spins around one axis one time a day, but spins around the other much slower.

If the user can make the Gyrotwister go fast enough, it can produce resistance enough to make it feel heavy, which in turn makes the user apply more energy, again making it go faster. Some variants, particularly one called XBeam, have a dynamo inside that produce patterns of light as the wheel spins around, and one can usually measure the speed at which the wheel is spinning by putting a microphone up to the device.

It's highly addictive, though it's not recommended in combination with excessive typing (e.g. noding) and certain auto-sexual practices.

Xbeam is currently known to be sold in Germany and Norway.

• http://www.gyrotwister.com/

If you put a gyroscope on the end of a hinged bar attached to a base that's free to rotate, with the hinged bar sticking a couple degrees off vertical something very interesting to watch happens. The whole assembly will rotate on it's base as the hinged bar with the gyroscope falls over.

You can also start the gyroscope with the bar horizontal and rotate the base back and forth by hand, and the hinged bar will move up and down.

I don't know where to begin with explaining the physics involved, but the gyrotwister works on a similar concept. As you change the angle (e.g. roll your wrist around) the gyroscope rotates radially (I.E. not along its axis) inside it's spherical casing. The spindle of the gyroscope is loosely fitted into a groove along the inside of the casing, and the radial motion in one axis increases the friction enough for there to be some grip between the spindle and it's guide track, while radial motion in the other axis rolls the spindle along in the guide track, accelerating the gyroscope.

Incidentally, don't be playing with one when you start trying to figure out how it works. You'll space out and when you come back to reality after your eureka moment your forearm will not feel well.

These aren't mere toys, though. My brother used one for physical therapy after he broke his arm.

Also sold under the name PowerBall.
http://www.power-ball.com