OCR · GCSE · Physics
Course version: J249 · Version from Sept 2018
Recall and apply: pressure (Pa) = force normal to a surface (N) / area of…
Full specification wording
Forces in action: recall and apply: pressure (Pa) = force normal to a surface (N) / area of that surface (m²) (content found only in the physics separate science qualification)
Pressure measures how concentrated a force is over a surface.
Checked against the OCR J249 specification (opens in a new tab) on .
- Point 5 of 21
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Pressure measures how concentrated a force is over a surface. The equation is p = F/A, where F is the force acting perpendicular (normal) to the surface, in newtons, and A is the area of that surface in square metres. The result is in pascals, where 1 Pa = 1 N/m². A force of 60 N spread over 0.03 m² gives p = 60 ÷ 0.03 = 2000 Pa. Only the normal component counts, so a force acting along the surface contributes nothing to pressure. A smaller area for the same force raises the pressure, which is why a sharp point or narrow heel presses harder. Convert areas to m² first: 1 cm² = 1 × 10⁻⁴ m², so 250 cm² = 0.025 m². This content appears only in the physics separate science qualification.
What earns the marks
- Selects the relationship pressure equals force normal to a surface divided by area of that surface.
- Identifies the force as the component acting perpendicular to the surface, in newtons.
- Uses area in square metres and states the pressure unit as the pascal, equal to one newton per square metre.
- Calculates pressure by dividing the normal force by the area, for example 60 N ÷ 0.03 m² = 2000 Pa.
- Converts an area given in square centimetres to square metres using the factor 1 × 10⁻⁴ before substituting.
Common mistakes and how to put them right
Uses the whole applied force when part of it acts along the surface.
Put it right: Resolve the perpendicular component first.
Substitutes an area in square centimetres without converting.
Put it right: Multiply by 1 × 10⁻⁴ to reach square metres.
Multiplies force by area instead of dividing.
Put it right: Divide the normal force by the area.
Reports the answer in newtons.
Put it right: Give pressure in pascals, which equal newtons per square metre.
Exam tips
- Write the equation, then list F and A with their units before substituting any numbers.
- Convert every area to square metres at the start so the pascal result follows directly.
- Check the answer by reasoning: halving the area for the same force should double the pressure.
Try the lesson
The start of the Forces in action: recall and apply: pressure (Pa) = force normal to a surface (N) / area of that surface (m²) (content found only in the physics separate science qualification) lesson, made from checked teaching notes for this specification point.
Have a go first
A force of 500 N acts normally on a surface of area 2 m². What pressure does the force produce on the surface?
Listen
Pressure measures how concentrated a force is over a surface. The equation is p = F/A, where F is the force acting perpendicular (normal) to the surface, in newtons, and A is the area of that surface in square metres. The result is in pascals, where 1 Pa = 1 N/m². A force of 60 N spread over 0.03 m² gives p = 60 ÷ 0.03 = 2000 Pa. Only the normal component counts, so a force acting along the surface contributes nothing to pressure. A smaller area for the same force raises the pressure, which is why a sharp point or narrow heel presses harder. Convert areas to m² first: 1 cm² = 1 × 10⁻⁴ m², so 250 cm² = 0.025 m². This content appears only in the physics separate science qualification. A strong answer earns marks for these points. Selects the relationship pressure equals force normal to a surface divided by area of that surface. Identifies the force as the component acting perpendicular to the surface, in newtons. Uses area in square metres and states the pressure unit as the pascal, equal to one newton per square metre. Calculates pressure by dividing the normal force by the area, for example 60 N ÷ 0.03 m² = 2000 Pa. Exam tip: Write the equation, then list F and A with their units before substituting any numbers.
See it
Key words
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Pressure as force per unit area
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Normal (perpendicular) force component
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Unit conversion of area to square metres
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The pascal as newtons per square metre
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See every definition
- Pressure as force per unit area
- Measures how concentrated a force is over a surface, found by dividing the force normal to that surface by the area of the surface.
- Normal (perpendicular) force component
- The force acting perpendicular to the surface; only this component counts, so a force acting along the surface contributes nothing to pressure.
- Unit conversion of area to square metres
- Areas must be converted to square metres first, using the factor 1 × 10⁻⁴, so that 250 cm² becomes 0.025 m².
- The pascal as newtons per square metre
- The unit of pressure, where 1 Pa = 1 N/m², so a force of 60 N over 0.03 m² gives 2000 Pa.
Label the diagram
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