# Physics behind the "Switch Pitch"?

I've come across this toy called a "Switch Pitch" designed by Chuck Hoberman. It's a ball that when tossed into the air (with some amount of rotation), inverts and changes colour. Made of plastic, it's connected with numerous sockets. It's quite hard to describe, so I'll include some links.

Here's a picture of the ball in first position, then midair, then in its second position.

A video of the ball being thrown. https://www.youtube.com/watch?v=zwevlig6CxI

I've done some research, and things like conservation of angular momentum, centripetal forces, translational energy, and rotational energy have come up (Also something about activation energy, though I believe that is chemistry). If these apply, could anyone explain how they do? I'm very curious about this.

Thank you!

• Nice question. Would be absolutely great if the concept of geometric (Berry) phase would play a role! Oct 11, 2014 at 7:22
• I've had one of those! I always thought the bits which turn the ball into a star (best description I can come up with) in mid-air were weighted so that when you applied the 'spin' to it they'd be forced outwards, the lapse in motion as it fell closing it into a different coloured ball- it's cool even without the physics though. Oct 11, 2014 at 7:34
• I'm sure J. J. Thomson or Alfred Mayer would use this as a "possible" classical model of neutrino oscillations, if they were alive today. ;) eoht.info/page/Floating+magnets+experiment Nov 1, 2016 at 20:03

Is a nice design, although it seem rather complex it only has one degree of freedom related to the expansion.

So it is a ingenious ensemble of pieces that are connected to each other in such a way that the system is only stable in 2 configurations.

Is composed of two types of pieces:

• disc-like piece: there are 4 of them visible for each color, they are surrounded by 3 of the other type:

• foil-like: they surround each disc-like piece when the ball is contracted

Going from one configuration to the other involves the hiding of 4 disc-like pieces, the surfacing of the other 4 that were hidden inside, and the flipping of all the foil-like pieces.

Why does this happen when rotating? Well this is caused by the centrifugal forces created when to the ball rotates. And it does not matter the direction of the rotation because when you pull one piece outside to expand, all the pieces move together due to all their movements being coupled. That is what it means that it has only one degree of freedom.

Why does it contract again? Well the ball can only expand certain amount due to its design, at this point it bounces back and starts a contraction movement folding again.

The details of the design are rather out of my design-drawing skills and I did not find better images or diagrams of the actual toy to produce here. I hope the explanation was graphic enough.