Cool Bed

Gizmodo has another cool gadget, a levitating bed. For those who know such a simple levitating system should be very unstable, you needn't worry as they've secured it laterally to the walls. For those that don't, you can read a bit more at the Wikipedia.

The short explanation starts with the idea of a magnet floating above another one, say. The gravitational and magnetic forces have the same magnitude and cancel (as can be measured by observing zero acceleration...my students always think the magnetic force must be greater than the gravitational, but then the magnet would be zooming off into space). Anyway, say this magnet is perfectly balanced laterally. Fine, but you can see it's unstable by considering any small deviation from perfectly balanced. Say a slight breeze pushes it left just a bit. Does it come back to center? No, because now there's even more of the bottom magnet to the right pushing the levitating magnet to the left. So instead of coming back, it just gets pushed off further left. Hence, it is unstable.