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Science at key stage 3 (Year 9)
Unit 9L: Pressure and moments
Section 1: a. What is pressure?
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Objectives |
| Children should learn: |
- how the effect of a force depends on the area to which it is applied
- how to use the quantitative relationship between force, area and pressure
- about practical applications of this relationship
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Activities |
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Outcomes |
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Children: |
- Elicit pupils' ideas about what it would feel like to lie on a bed of nails and whether they would rather have their foot trodden on by an elephant or by someone wearing stiletto heels. Draw the conclusion that the area over which a force is concentrated makes a difference to its effect. State the relationship: pressure = force÷area (perpendicular to direction of force).
- Ask pupils to work out the lowest and highest pressure they can exert on a part of their body. This requires them to weigh themselves in newtons and measure the cross-sectional area of any part of their body on which they are capable of balancing,
eg head, tiptoes, hands, full body.
- Ask pupils to contribute to a list of devices that rely on low pressure being exerted,
eg snowboards, snowshoes, camels' feet, and a list where high pressure is required,
eg blades, drawing pins. Demonstrate or show video clips of some of these.
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- explain the relationship between force and area,
eg in terms of lying on a bed of nails
- apply the quantitative relation between pressure, force and area to a number of situations,
eg skis, sharp blades
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Points to note |
- Pressure is, technically, a hydrostatic process, ie the forces act in all directions. This is dealt with below in pneumatics and hydraulics. The concept described here is where the force is in one direction only, more precisely termed
'stress'. However, this treatment follows common usage of the term
'pressure'.
- Encourage pupils to distinguish between the terms
'force' and
'pressure', and avoid saying the 'pressure is concentrated' instead of 'the force is concentrated'.
- It is acceptable to use units of Ncm-2, though pascals may be used.
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This unit is divided into sections. Each section contains a sequence of
activities with related objectives and outcomes. You can view this unit by
moving through the sections or print/download the whole unit.
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