The Toy thought to Defy Science!
Meet the Tippe Top, a toy that has fascinated scientists for over a century. Discovered by German physicist Helen Sperl in 1891, once it starts to spin on its rounded head it soon flips over to spin on its stem. And that’s not all, once it inverts it starts to spin in the opposite direction!
The top, whose popularity grew rapidly all over the world during the 1950's, has been the subject of several theoretical articles. Since the Tippe Top raises its center-of-mass, the top will need to get its necessary potential energy by spinning slower after inversion. This means that the angular momentum has been reduced, and this is only possible by applying an external torque, which can only come from friction. So how does the Tippe Top work?
A Tippe Top works because its center-of-mass does not coincide with the geometrical center of sphere. Since the rotational axis goes through the center-of-mass, the top will slide over the surface on which it is spinning. The sliding friction supplies the torque needed for the inversion of the top.
At some point during the inversion, the top stops spinning around the axis through the stem and then starts to rotate the other way. At the same time, the center of mass is lifted, and the top thus presents an interesting problem concerning conservation of energy and angular momentum.
Perhaps, the fascination that physicists have had with this toy is best brought out by this famous picture which exists from the opening of the institute of physics at the University of Lund in Sweden in 1951, where Wolfgang Pauli and Niels Bohr are looking at a Tippe Top!
Watch our Tippe Top video here: