Alien rock?

[RayPV]

Seems like it would be easy to fake this

[Nick Theodorakis]

Might be a lodestone, so it's trying to align with the Earth's magentic field.

Nick

[GenYus234]

But it only seems to reverse when spun in one direction. Also, would a lodestone have enough force to stop and reverse that quickly?

I was thinking something to do with the shape. When spun, the unbalanced nature means that it has a center of centrifugal force that is offset from the center of balance. This could cause it to tip up a slope on the underside to a new balance point. When it slows, the loss of centrifugal force makes it shift back to the previous center point. If the slope is just right, this could impart reverse spin on it.

[mags]

It is awfully strange that it starts to move the first time before it is touched. I think it is a combination of a hidden magnet, and quirk of its shape. Like a "rattleback" which have apparently been around a long time : http://en.m.wikipedia.org/wiki/Rattleback

Eta: current toy that exploits this concept: http://www.scientificsonline.com/space-pets.html

[Der Induktionator]

I have a couple of those, they behave exactly the same as the alien stone in the video.

[Jim18655]

I have a plastic one. Called a "Rattle-back. " Spin in one direction and it stops and reverses rotation.

[nonnieyrissa]

I was liking t has a few similar holes on the side that is not shown and you could put a few small but strong magnets. Maybe neodymium. The way it is shape it going to make turning against the edge hard but into the curve east as there isn't nearly as much friction.

[ganzfeld]

It's just an ordinary rattleback (see mags' link). It looks like it moves a couple of times without being touched but it's just rocking in the direction the rattleback likes to turn. The first time it looks like it moves on its own but he actually brushes the tip with his thumb ever so slightly and it moves easily in the direction it 'prefers' so quickly (away from the thumb) that it looks like his thumb didn't do it.

[nonnieyrissa]

I didn't notice his thumb hitting it when I watched it before, I had just assumed it was a rattleback that also had a small yet strong enough magnet to get t initially started. I see where he slightly brushes it though.

[Penguin!]

I used to have a plastic one of these. There were no magnets to it at all and it would spin very easily in one direction, but when pushed in the other direction, it would slow and spin the other way. It looks like it is just curved on the bottom, but when you look at it closer, the apex (?) of the curve is slightly off center.