Physics·General Physics · NSSCO 2.11
Pressure in solids & liquids
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Pressure is how concentrated a force is — how hard it pushes on each little bit of a surface. In this lesson we meet P = F ÷ A and its unit the pascal, see why a smaller area gives a bigger pressure, use the clever trick of hydraulic machines, work out how pressure grows with depth using Δp = ρgΔh, and finish with the pressure of the air around us — how it changes with altitude, how we measure it, and how it makes the wind blow.
What you'll learn in this lesson
By the end you should be able to (NSSCO Physics 2.11):
- Define pressure as the perpendicular force acting on a unit area, and recall and use P = F ÷ A (unit: pascal, Pa = N/m²; and kilopascal, kPa)
- Interpret the relationship between pressure, force and area — explain what happens when the force or the area is changed
- Describe and explain the transmission of pressure in hydraulic systems, with reference to hydraulic brakes and hydraulic jacks
- State that the pressure beneath a liquid surface increases with depth and with density
- Derive, recall and use the equation Δp = ρgΔh
- Describe how atmospheric pressure changes with altitude, and use a manometer to measure pressure
- Perform calculations involving the interconversion of units of pressure (mm Hg, Pa)
- State that a wind is caused by high and low pressure systems
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