PHYSICS · Stage 8 · Chapter 6: Forces, Motion and Pressure
Physics 6.15 Using pressure — High and Low Pressure Applications
5 min read 5 parts Lesson 15 of 19
Lesson summary
Physics 6.15 Using pressure — High and Low Pressure Applications — Alhussan International Academy — Physics (Stages 7–9) notes: Explain how increasing or reducing the area over which a force acts is useful.Principle — Pressure depends on force and area (P = F ÷ A), and designers …
- Large area
- Small area
- Knives and scissors
- Other tools
- Sharpening
- Handles and straps
Section 1 of 5Controlling pressure
- Principle
- Pressure depends on force and area (P = F ÷ A), and designers usually change the area because the force is fixed.
- Large area
- The force is spread out, so pressure is low and the surface is not damaged.
- Small area
- The force is concentrated, so pressure is high and surfaces can be cut or pierced.
Section 2 of 5Where large pressure is useful
- Knives and scissors
- The blades have a very small area, so the force applied produces a large pressure.
- A blunt blade has a bigger area, so the pressure may be too small to cut.
- Nails
- The pointed end has a tiny area, so a hammer blow produces a very large pressure that pushes it in.
- Other tools
- Needles, axes, drawing pins and saw teeth have sharp edges or points for the same reason.
- Sharpening
- Making an edge thinner reduces its area, so the same force gives more pressure.
Section 3 of 5Where small pressure is useful
- Handles and straps
- Wide carrier-bag handles and rucksack straps spread the force over a big area, which is more comfortable.
- Soft ground
- A surface such as sand or mud can be sunk into if the pressure is too high.
- Wading birds have wide flat feet so they do not sink much.
- Camels have large feet, so it is easier for them to walk on sand than for horses with small hooves.
- A horse can exert four times the pressure of a camel even though it weighs less, because its hooves have a smaller area.
- Other examples
- Snowshoes, skis, tank tracks and earthmover tracks spread weight over large areas.
Section 4 of 5Bike tyres
- Mountain (off-road) bike
- Wide tyres have a large contact area, so the pressure on soft ground is low and they do not sink.
- Road bike
- Narrow tyres touch the road over a small area, which suits a firm surface.
Section 5 of 5Choosing the right design
| Aim | How to change the area | Examples |
|---|---|---|
| Lower pressure | Increase the area | Wide handles, wide straps, snowshoes, tank tracks, mud-bike tyres |
| Higher pressure | Decrease the area | Knife, nail, needle, drawing pin |
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