Pressure = force ÷ area
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 4 worked examples, 7 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Why a knife cuts
- What is pressure?
- The equation, three forms
- Units of pressure
Read the transcript of the teaching part
Last time
Before we start: last time, in Power, efficiency and energy resources, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Why a knife cuts
A blunt knife and a sharp knife are pressed with the same force. The sharp one cuts, and the blunt one does not. The force is the same. What is different is the area it is pushed through. Pressure is what combines the two.
What is pressure?
Pressure is the force acting at right angles to a surface, for each unit of area of that surface. A big force on a small area gives a big pressure. The same force spread over a big area gives a small pressure. So pressure depends on two things: the force, and the area it acts on.
The equation, three forms
Pressure equals force divided by area. For the force, multiply pressure by area. For the area, divide the force by the pressure. Write the one you need, then substitute.
Units of pressure
Force is measured in newtons and area in square metres. So pressure is in newtons per square metre. That unit is called the pascal, Pa. A pascal is tiny, so we often use the kilopascal, which is one thousand pascals. Cambridge sometimes uses newtons per square centimetre. Then the area stays in square centimetres.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Pressure = force ÷ area.
Chapter 1.8: Pressure
- Pressure = force ÷ area 6 min
- Pressure in liquids and the atmosphere 6 min
Also for O Level Physics 5054
Which topics come up most in O Level Physics 5054 past papers, counted from every paper since 2004.