Gravesande's Ring

Gravesande’s ring is an apparatus for demonstrating thermal expansion and contraction, a fundamental principle in thermodynamics.

Named after Dutch scientist Willem Gravesande, the apparatus consists of two main components: a brass ring, and a brass ball slightly smaller in diameter than the ring. The ball can pass freely through the ring when both are at the same temperature. However, when the ball is heated, it undergoes thermal expansion and no longer fits through the ring. Once it cools down, it contracts and is again able to pass through.

At a microscopic level, when the brass ball is heated, the kinetic energy of its molecules increases. This heightened energy causes the molecules to vibrate more vigorously and take up more space, leading to an increase in the overall size of the ball.

The demonstration could also be reversed by cooling the ring instead of heating the ball. When the ring is cooled, its molecules lose kinetic energy and vibrate less intensely, causing the ring to contract slightly. If cooled enough, the ring’s diameter would decrease to the point where the previously fitting ball can no longer pass through.