Animated cartoon of Tomlinson's mechanismus. At a certain position of the support, the position of the tip becomes unstable and a sudden jump occurs.

When a tip is dragged over a periodic potential through an elastic medium (symbolized as a spring), at certain positions of the support the tip may undergo sudden jumps. It is impossible to drag the tip in a fully controlled way. Hence the tip is unable to follow the support adiabatically. In the Playing Tomlinson section you may experience this fact yourself.