A person has roughly the same weight whether wearing trainers or high heels, but the force can be spread over very different areas. Pressure equals force divided by area. A narrow heel places part of the person's weight onto a tiny contact area, creating a very high pressure. A trainer spreads the force across a much larger sole, so the pressure on the floor is lower. Soft flooring can therefore dent more easily under a thin heel. This is the same physics that allows snowshoes to reduce pressure on snow by increasing contact area.

Engineers use this relationship when choosing shapes and contact areas. Ships, hydraulic systems, tyres, foundations and cutting tools may look unrelated, but each is designed around how forces are spread through a material or fluid. Similar principles appear in nature too, from broad animal feet on soft ground to floating ice changing the conditions at the surface of a lake.

Pressure is the force acting on each square metre of area, so the same force can have very different effects depending on where it is applied. In liquids, pressure is transmitted through the fluid; this is why a small force on a small piston can produce a much larger force on a larger piston. The trade-off is distance: the larger piston moves a shorter distance, so the machine does not create energy from nowhere.