Sound is simply waves of pressure passing through a transmission medium such as water or air. The intensity – or loudness – of the sound depends on just how violently the material’s molecules are jolted by the pressure waves. When a leaf falls to the ground, the impact injects relatively little energy into the surrounding air molecules, so the molecules don’t move much. But when two hefty, fast-moving objects collide, the noise can literally be deafening.
Robert is a science writer and visiting professor of science at Aston University.