1.9Motion, Forces and Energy
Pressure — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions
10 min read 16 parts Lesson 89 of 91 Unit quiz
Lesson summary
1.9 Pressure (Part 1) — IGCSE PHYSICS notes: Define pressure, calculate it from force and area, and explain everyday applications of large and small areas.Definition — pressure is the force per unit area.p = F ÷ A, where p is pressure, F is force and A is area.Units — pressure is…
- Rearrangements
- Drawing pins
- High heels
- Pressure in a liquid pump
- Force on the piston
- Large area gives large force
Part 1 of 7Definition of pressure
Definition
- Definition pressure is the force per unit area.
- p = F ÷ A, where p is pressure, F is force and A is area.
Units
- Units pressure is measured in N/m2, which equals the pascal (Pa).
- 1 N/m2 = 1 Pa, and N/cm2 is also used when area is in cm2.
Rearrangements
- F = pA and A = F ÷ p.
Part 2 of 7What the equation tells us
| Situation | Result |
|---|---|
| Same force, larger area | Smaller pressure |
| Same force, smaller area | Larger pressure |
| Several points of contact | Add their areas to get the total area |
| Double the force, same area | Pressure doubles |
Part 3 of 7Applications
Tractors
- Tractors large tyres spread the weight over a large area, which lowers the pressure so the tractor does not sink into mud.
Drawing pins
- Drawing pins the sharp point has a tiny area, so the force from your thumb makes a large pressure that pushes into the wall.
High heels
- High heels the small heel area gives a high pressure, so they sink into soft ground more easily than flat shoes carrying the same weight.
Part 4 of 7Method for pressure calculations
1
List the force (a weight is mg) and the area.
2
Convert units, such as cm2 to m2 or keep cm2 for N/cm2.
3
Add the areas if there are several contact points.
4
Use p = F ÷ A, or F = pA if the pressure is given.
5
Round to a sensible number of significant figures and state the unit.
Part 5 of 7Hydraulic systems
Hydraulic systems
Pressure in a liquid pump
- Pressure in a liquid pump a pump creates a pressure in the liquid that acts on a piston.
Force on the piston
- Force on the piston the force equals the pressure multiplied by the piston's area.
Large area gives large force
- Large area gives large force this is why hydraulic lifts can raise heavy platforms.
Part 6 of 7More about pressure
1Same weight, different pressure
- Same weight, different pressure a person standing on one foot exerts double the pressure of standing on two.
2Other applications
- Other applications caterpillar tracks, wide tyres, skis and snowshoes all lower pressure with a big area.
3Sharp tools
- Sharp tools knives, nails and needles raise pressure with a tiny area.
4Unit conversions
- 1 m2 = 10 000 cm2, so 1 N/cm2 = 10 000 Pa.
Part 7 of 7More from the specification
1Pressure distribution across fluid boundaries
- Pressure distribution across fluid boundaries static fluids exert isotropic normal forces per unit area perpendicular to container walls.
2Pressure definition and formula
- Pressure is perpendicular force per unit contact area: p = F / A, measured in pascals (1 Pa = 1 N/m2.
3Hydrostatic liquid pressure
- Pressure in liquids increases directly with depth and density: delta p = rho g delta h, acting equally in all spatial directions at a given depth.
4Hydraulic machines and force multiplication
- Liquid incompressibility allows hydraulic systems to transmit pressure equally;
- a small input force on a small piston creates a large output force on a large piston.
5Hydrostatic fluid pressure
- Hydrostatic fluid pressure fluid pressure equation Δp = ρ g h describes how pressure increases linearly with liquid density and column depth.
6Pressure units definition
- Pressure units definition pressure equals force in newtons acting perpendicularly over an area of one square metre, yielding pascals.
7Atmospheric pressure contribution
- Atmospheric pressure contribution total pressure on an object submerged in water equals atmospheric surface pressure added to liquid column pressure.
8Atmospheric pressure
- Pressure of the air, about 1.01 × 105 Pa at sea level.
9Gravitational field
- Region where mass experiences gravitational force.
10Field strength
- G = Fg/m.
11Density
- Mass per unit volume.
12Newton
- Unit of force, kg m s-2.
Key terms
| Term | Meaning |
|---|---|
| Pressure | Force per unit area. |
| Pascal (Pa) | The unit of pressure, one newton per square metre. |
| Area | The size of a surface, measured in square metres. |
| Hydraulic | Using a liquid under pressure to transmit force. |
| Contact area | The area over which a force is spread. |
Avoid these mistakes
1
Forgetting to add the areas of all the legs or feet.
2
Using the wrong area unit with N/m².
3
Explaining pressure with friction or stability.
4
Saying a bigger force always means a bigger pressure — the area matters too.
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