Pressure depends on force and area — Physical education, 11–13 years
Pressure describes how concentrated a force is over an area. The same force can have a gentle or powerful effect depending on how much surface receives it.
Force spread over an area
Pressure is the amount of force acting on each unit of area. A sharp drawing pin makes high pressure because its point gives the force a tiny area. A wide snowshoe makes lower pressure because a person’s weight spreads over more snow.
Why use pressure?
Saying only “a force acts” does not tell us how strongly a surface is affected. The same force can dent a table or barely touch it, depending on its area. Pressure was developed as a useful comparison for cutting, pressing, supporting and understanding fluids.
A shoe on the floor
A person pushes down with 600 N. If the soles touch the floor over 0.030 m², the pressure is 600 ÷ 0.030 = 20,000 Pa. If the same force acts through a 0.003 m² heel, the pressure is 200,000 Pa, ten times greater.
More area, more pressure?
Many people expect a wider surface to create more pressure because it touches more of the object. That is reasonable when thinking about total contact, but pressure is force divided by area. With the same force, spreading it over a larger area lowers the pressure at each place.
Tools that concentrate pressure
Knives, needles and nails work because their sharp ends put a force onto a very small area. Car jacks do the opposite in a different way: they use pressure in a fluid to transmit a force and lift a heavy vehicle. Pressure also helps explain why wide tyres are useful on soft ground.
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