Pressure depends on area — Physics, 7–10 years
The same force can have different effects when it acts on a small or large area. This explains sharp points, wide feet and many everyday designs.
Force spread over space
Pressure tells us how concentrated a force is on a surface. The same force makes more pressure when it is packed into a small area, and less pressure when it is spread over a large area. It is not a new kind of force; it is a way to describe its effect on a surface.
Why this matters
People needed to understand why a knife cuts with its edge but a hand does not cut when pressing with its palm. The force may be similar, yet the contact area is very different. Thinking about pressure helps us choose shapes that grip, cut, support or protect without simply using a bigger force.
Two shoes in snow
Imagine your weight pushes down with 600 newtons. One ordinary shoe touches the snow over 0.02 square metres, so both shoes touch 0.04 square metres. Pressure is 600 ÷ 0.04 = 15,000 pascals. Snowshoes spread the same weight over 0.20 square metres: 600 ÷ 0.20 = 3,000 pascals, so you sink less.
The pressure mistake
A reasonable mistake is thinking that a larger object always makes more pressure. Size alone is not enough: we must know the force and the area touching the surface. A heavy box on a wide base may make less pressure than a lighter box balanced on a narrow edge.
Where it appears
Needles and drawing pins have tiny points, concentrating force so they enter material. Wide tyres, skis and the feet of some furniture spread force so they do not sink easily into soft ground. Builders use both ideas when designing foundations, tools and protective equipment.
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