Pressure: force spread over area

4 minAS Level4.3.2

AI-drafted, independently checked · not yet teacher-reviewed

By the end of this lesson

By the end, you can define pressure as normal force per unit area and calculate pressure, force or area.

Definition

Pressure

Pressure is the force acting normally per unit area. “Normally” means at right angles to the surface.

The area changes the pressure

Push the same way on a wide pad and a narrow pin. The force can be the same, but the pin applies it to a much smaller area, so its pressure is greater.

Call the pressure $p$ . Let $F$ be the force at right angles to the surface and $A$ the area it acts on. Then:

$p = \dfrac{F}{A}$

Pressure is measured in pascals, $\text{Pa}$ ; $1\ \text{Pa}=1\ \text{N m}^{-2}$ .

Quick check

Multiple choiceQuestion 1 · Recall

Which quantity belongs in the definition of pressure?

AForce acting normally per unit area.BAny force per unit length.CForce multiplied by area.DMass per unit area.

CalculateQuestion 2 · Apply

A normal force of $240\ \text{N}$ acts over $0.012\ \text{m}^2$ . Calculate the pressure.

Answer the 2 questions above to continue.

Previous lessonDensity: mass packed into space Next lessonWhere the liquid-pressure equation comes from

The same force over less area gives greater pressure.