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Pressure in solids, liquids and gases
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Why do snowshoes stop you sinking, and why do your ears pop in a plane? It is all about pressure.
Pressure on surfaces
pressure = force ÷ area, acting at right angles (normal) to a surface.
Pressure is measured in pascals (Pa). 1 Pa = 1 N/m². You may also see N/cm².
The same force on a smaller area gives a bigger pressure: a sharp knife cuts easily. A larger area gives a smaller pressure: snowshoes spread your weight so you do not sink.
Pressure is measured in pascals (Pa). 1 Pa = 1 N/m². You may also see N/cm².
The same force on a smaller area gives a bigger pressure: a sharp knife cuts easily. A larger area gives a smaller pressure: snowshoes spread your weight so you do not sink.
Pressure in liquids
Pressure in a liquid increases with depth, because there is more liquid above pushing down. Dams are thicker at the bottom for this reason.
The pressure is bigger on the bottom of an object in water than on its top. This difference gives an upward force called upthrust.
An object floats if the upthrust can balance its weight. If its weight is bigger than the upthrust, it sinks.
The pressure is bigger on the bottom of an object in water than on its top. This difference gives an upward force called upthrust.
An object floats if the upthrust can balance its weight. If its weight is bigger than the upthrust, it sinks.
Atmospheric pressure
The air above us has weight, which causes atmospheric pressure.
The higher you go, the less air there is above you, so atmospheric pressure decreases with height. That is why your ears can pop when a plane climbs.
The higher you go, the less air there is above you, so atmospheric pressure decreases with height. That is why your ears can pop when a plane climbs.
A box with a weight of 600 N rests on a base of area 2 m². What pressure does it exert on the floor?
- pressure = force ÷ area
- pressure = 600 ÷ 2
Answer: 300 Pa
Pressure = force ÷ area, in pascals (N/m²). Smaller area, bigger pressure. Liquid pressure increases with depth and causes upthrust; objects float when upthrust balances weight. Atmospheric pressure decreases with height.
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