AQA · GCSE · Physics

    Course version: 8463 · Version from Sept 2016

    Pressure in a fluid 1: pressure, p, in pascals, Pa

    Pressure, p, measures how concentrated a force is over an area and is measured in pascals, Pa.

    Checked against the AQA 8463 specification (opens in a new tab) on .

    • Point 6 of 9
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Pressure, p, measures how concentrated a force is over an area and is measured in pascals, Pa. One pascal is equal to one newton per square metre (1 Pa = 1 N/m²). In a fluid (a liquid or a gas), this pressure causes a force that acts at right angles (normal) to any surface it contacts, such as the walls of a container. To use the quantity, select the equation p = F ÷ A, ensure the area is in square metres (for example, converting 250 cm² to 0.0250 m²), substitute the values, and state the final answer with the unit Pa or N/m². Always state pressure with a valid unit, and ensure the force used is perpendicular to the surface.

    What earns the marks

    • State that the unit of pressure is the pascal (Pa) and that 1 Pa = 1 N/m².
    • Identify that fluids (liquids and gases) exert pressure that causes a normal force on surfaces.
    • Use p = F ÷ A correctly, including rearranging to F = p × A or A = F ÷ p.
    • Convert areas into square metres before substituting, for example 250 cm² = 0.0250 m².
    • Give answers with the correct unit, Pa or N/m², and recognise that the force acts at right angles to the surface.

    Common mistakes and how to put them right

    • Using the area in cm² without converting to m², which makes the calculated pressure too small.

      Put it right by dividing the cm² value by 10,000.

    • Quoting the answer for pressure in newtons (N).

      Put it right by checking that the calculation divides force by area and the unit is Pa or N/m².

    • Forgetting that fluids include both liquids and gases.

      Put it right by applying the pressure equation to both gas containers and liquid vessels.

    Exam tips

    • Write the equation p = F ÷ A, substitute values with units, then give the answer in Pa to an appropriate number of significant figures.
    • When a question gives an area in cm² or mm², convert to m² first and show the conversion clearly to secure method marks.

    Try the lesson

    The start of the Pressure in a fluid 1: pressure, p, in pascals, Pa lesson, made from checked teaching notes for this specification point.

    Have a go first

    Pressure is measured in pascals (Pa). Which of the following is equivalent to one pascal?

    Listen

    Pressure, p, measures how concentrated a force is over an area and is measured in pascals, Pa. One pascal is equal to one newton per square metre (1 Pa = 1 N/m²). In a fluid (a liquid or a gas), this pressure causes a force that acts at right angles (normal) to any surface it contacts, such as the walls of a container. To use the quantity, select the equation p = F ÷ A, ensure the area is in square metres (for example, converting 250 cm² to 0.0250 m²), substitute the values, and state the final answer with the unit Pa or N/m². Always state pressure with a valid unit, and ensure the force used is perpendicular to the surface. A strong answer earns marks for these points. State that the unit of pressure is the pascal (Pa) and that 1 Pa = 1 N/m². Identify that fluids (liquids and gases) exert pressure that causes a normal force on surfaces. Use p = F ÷ A correctly, including rearranging to F = p × A or A = F ÷ p. Convert areas into square metres before substituting, for example 250 cm² = 0.0250 m². A common slip: Using the area in cm² without converting to m², which makes the calculated pressure too small. Instead, dividing the cm² value by 10,000. Exam tip: Write the equation p = F ÷ A, substitute values with units, then give the answer in Pa to an appropriate number of significant figures.

    See it

    A top-down flowchart. The top node reads 'Pressure, p'. From it, three branches lead down. The first branch goes to 'Measured in pascals, Pa', which leads to '1 Pa = 1 N/m²'. The second branch goes to 'Equation: p = F ÷ A', which splits into three: 'Rearrange to F = p × A', 'Rearrange to A = F ÷ p', and 'Convert area to square metres first', the last of which leads to 'Example: 250 cm² = 0.0250 m²'. The third branch goes to 'Fluids (liquids and gases) exert pressure', which leads to 'Force acts at right angles (normal) to the surface'.
    It shows what pressure is, its unit, the equation p = F ÷ A with its rearrangements and area conversion, and that fluids exert a normal force on surfaces.

    Key words

    Say what each word means before you turn the card.

    Pressure

    Try answering aloud or in your head before turning the card.

    Pascal (Pa)

    Try answering aloud or in your head before turning the card.

    Fluid pressure

    Try answering aloud or in your head before turning the card.

    Equation for pressure

    Try answering aloud or in your head before turning the card.

    See every definition
    Pressure
    Measures how concentrated a force is over an area and is measured in pascals, Pa.
    Pascal (Pa)
    The unit of pressure, where one pascal is equal to one newton per square metre (1 Pa = 1 N/m²).
    Fluid pressure
    In a fluid, a liquid or a gas, pressure causes a force that acts at right angles (normal) to any surface it contacts.
    Equation for pressure
    p = F ÷ A, which can be rearranged to F = p × A or A = F ÷ p.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. The top node reads 'Pressure, p'. From it, three branches lead down. The first branch goes to 'Measured in pascals, Pa', which leads to '1 Pa = 1 N/m²'. The second branch goes to 'Equation: p = F ÷ A', which splits into three: 'Rearrange to F = p × A', 'Rearrange to A = F ÷ p', and 'Convert area to square metres first', the last of which leads to 'Example: 250 cm² = 0.0250 m²'. The third branch goes to 'Fluids (liquids and gases) exert pressure', which leads to 'Force acts at right angles (normal) to the surface'.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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