To demonstration the principle of center of gravity.
1. Glass tumbler
2. Two steel forks
When the prongs of two forks are intersected by inserting a coin between the prongs so that it holds both forks together, you will be able to balance the coin and forks on the rim of a glass. The entire weight of both forks appears to be on the outer portion of the coin but the forks and coin don?t fall. The reason is because the heavy handles of the forks curve inwards towards the glass tumbler, hence this shifts the centre of gravity of the entire structure to a point directly beneath the spot where the coin rests on the glass tumbler. This results in the forks and coin attaining a state of stable equilibrium through their center of gravity.