The Spinning - Top

If we make the top spinning, it stands up on its little foot. The reason of this extraordinary behaviour is not so clear know; friction is a decisive factor.

The energy dissipated under the influence of the friction's force is bigger if the spinning-top spins on its larger pole (medium moment of friction force is bigger at equal pressure). Therefore, the spinning-top tends to reduce the friction surface at the cost of rising its barycentre. The enhancement of potential energy is possible by a reduction of the rotation speed.

Lofty physicists (Niels Bohr and Wolfgang Pauli) tried to finds tips on this top already at the beginning of XX century. The exact solution is far from being easy.

In contrast with 'regular' spinning tops, always with a pointed foot and performing precession under the influence of gravitation, the tippe-top suffers mainly from friction forces. These are frinction forces which cause it raising upside-down. After the tippe top inverts its position it rotates more slowly - some of its kinetic energy of rotation has been used to move the centre of mass up. The difference in angular momentum is absorbed by 'the universe', i.e. by the floor which is the source of friction force.

In contrast with the gyroscope, the symmetry axis in the tippe top it is free to change its direction. For this reason the upside-down revolution of tippe-top and gyroscope are different. For an external observer, after the upside-down revolution, the gyroscope rotates in the opposite sense, whereas a tippe top rotates in the same direction; only for a brownie inside a tippe top it rotates in the opposite direction.

Finally, let us observe that 'regular' spinning tops, are not that fully symmetric solid bodies, they are either spindle- or rotund-shaped, they are hardly ever spherical as the tippe top.