Pressure

Pressure is how concentrated a force is: the force divided by the area it pushes on, pressure = force ÷ area, or P = F/A. Its unit is the pascal (Pa), one newton on every square metre. The same force on a small area makes a big pressure, which is why a drawing pin goes into wood, a sharp knife cuts and a stiletto heel marks a floor. Spread over a large area it makes a small pressure, which is why skis keep you on top of snow, tractors have wide tyres and a building stands on broad foundations.