Pressure
Why can you walk on snow in snowshoes, but sink in your boots?
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Explain
Sharp points press hard.
Wide feet stop you sinking.
Pressure is how strongly a force presses on each bit of an area.
The same force on a small area makes high pressure. On a big area it makes low pressure.
That's why drawing pins go in easily, and why snowshoes stop you sinking.
P = F / A. The unit is the pascal (Pa), which is one newton per square metre.
Liquids and gases also press in all directions. Pressure rises with depth.
Worked example: 500 N on 0.05 m² gives 10 000 Pa. On snowshoes of 0.5 m², it gives 1000 Pa.
- Same force
- Smaller area
- More pressure
Want the full story?
Pressure in a liquid depends on depth: P = ρgh. Every 10 m of water adds about the pressure of the whole atmosphere. The areas in the sim are rough values.
The Formula
pressure = force ÷ area
- the pressure, measured in pascals (Pa)
- the force, measured in newtons (N)
- the area it presses on, measured in square metres (m²)
Try the numbers
Pressure: 10,000 Pa
Try it at home
You need a tray of flour, a pencil, a flat block.
You need: a tray of flour, a pencil, a flat block.
Press a finger in flour, then your whole hand.
- Fill a tray with flour.
- Press a pencil end into it, gently.
- Press a flat block with the same force, and compare.
What's happening: the same force on a smaller area makes more pressure, so the pencil sinks further.
Physics is life
Your body
Your blood is under pressure.
Daily life
Knives are sharp to press hard.
Nature
Camels have wide feet.
Space
Astronauts wear pressure suits.
Quick check
Question 1 of 3
Words to know
Pressure: How much force presses on each bit of area.
- Pressure
- How much force presses on each bit of area.
- Pascal (Pa)
- The unit of pressure. One pascal is one newton on each square metre.
- Force
- A push or a pull on something.