Pressure is the force acting on each unit of area. The SPM Physics pressure chapter covers solids, liquids, gases, Pascal’s principle, Archimedes’ principle and the effects of fluid flow.
This page sits under SPM Physics. It shows the order to study, one short example, and where to begin.
How do the pressure lessons connect?
Everything grows from one idea: pressure = force ÷ area. Start with calculating pressure in solids and liquids, then move to comparing pressure at different depths.
Once depth makes sense, Pascal’s principle follows, because it says pressure in a closed liquid is passed on equally. Archimedes’ principle uses the same depth idea to explain buoyancy.
The last lesson, fluid-flow effects, is about explanation rather than calculation. Test yourself with the pressure practice set.
What does one example look like?
A worked example: a rectangular tank holds water 0.50 m deep and has a base of 0.40 m × 0.20 m. Use ρ = 1000 kg m⁻³ and g = 10 N kg⁻¹.
The pressure from the water on the base is ρgh = 1000 × 10 × 0.50 = 5000 Pa. The area of the base is 0.08 m², so the force on it is 5000 × 0.08 = 400 N.
A sealed piston pushing down on the water with an extra 200 Pa adds 200 Pa everywhere in the liquid, which is Pascal’s principle. A wooden block floating in the tank displaces its own weight of water, which is Archimedes’ principle. One tank, three ideas.
Where should you start?
If you mix up force and pressure, begin with the first lesson and do not skip the unit conversions. If calculations are fine but explanations lose marks, go straight to the fluid-flow lesson.
A student who can do every lesson but freezes on mixed questions will gain most from the practice set. You can also read how the subject is taught in online one-to-one SPM Physics tuition.