Year 7 Science · Unit 3 · Lesson 8
Extension · Foundation Worksheet
Learning Goals
Extension · optional
Pressure sits beyond the Stage 4 Forces dot points this unit is built on, and is met properly in later years. Nothing on this sheet is assessed as part of Year 7 Forces, so it is enrichment rather than required practice. Do it if you are interested, and skip it without losing any marks if you are not.
Fill the gap
Choose the correct word from the word bank. Each word is used at most once. Two words are not needed: cross them out.
Pressure is the effect of a spread over an area. If the same force acts on a area, the force is more and the pressure is higher. If the same force acts on a area, the force is and the pressure is lower. That is why a person wearing snowshoes stays on top of soft snow, but a person in ordinary boots into it.
1. A drawing pin has a flat head and a sharp point. When you press it into a corkboard, which end goes in? Use the words pressure and area in your answer.
Odd one out
In each set, three things do the same job with pressure and one does the opposite. Circle the odd one out, and say whether it makes pressure high or low and why.
| Set | Circle the odd one out |
|---|---|
| 1 | snowshoes · wide tractor tyres · a stiletto heel · a camel's wide hoof |
| 2 | a sharp knife edge · a drawing pin point · a pointed tent peg · an elephant's flat foot |
| 3 | wide backpack straps · a red kangaroo's long, flat hind feet · a sewing needle · a wide plank laid across mud |
2. Two tent pegs are hit with the same hammer blow. One is pointed and one has a flat end. Draw both pegs, with an arrow for the force and a label on each contact area. Then explain why the pointed peg goes into the ground more easily.
Read the data
Scenario: footprints in damp sand
Jess weighs 500 N. She stands still for 10 seconds on a flat patch of damp sand, wearing something different each time. When she steps off, the class measures how deep her print is.
| What Jess stood on | Contact area with the sand (cm²) | Depth of print (mm) |
|---|---|---|
| One bare foot | 150 | 16 |
| Two bare feet | 300 | 9 |
| Two wide, flat beach shoes | 450 | 6 |
| Two snowshoes | 1800 | 1 |
Source: sample class results.
3. Describe the pattern in Table 1. What stayed the same in every test?
4. Jess now stands on the toes of one bare foot, a contact area of about 40 cm². Predict whether her print will be deeper or shallower than 16 mm, and explain your prediction using pressure.
5. The lesson says a 60 kg person in stiletto heels can press harder on a floor than a 3000 kg elephant. The elephant stands on four flat feet with a total area of about 2000 cm². The stiletto heel tip has an area of about 1 cm². Explain how the person can make more pressure.
Fill the gap
force; smaller; concentrated; larger; spread out; sinks. Not used: heavier, faster.
Question 1
The sharp point (1). The same force acts at both ends; the point's tiny area gives a very high pressure, while the flat head's large area gives a low pressure on your thumb (1). [2 marks]
Odd one out
1 each. 1. The stiletto heel: tiny area, high pressure; the others spread weight to keep pressure low. 2. The elephant's flat foot: large area, low pressure; the others concentrate force to cut or pierce. 3. The sewing needle: tiny point, high pressure to pierce cloth; the others spread force to keep pressure low. [3 marks]
Question 2
Two pegs drawn with a force arrow on each and the tip areas labelled, small and large (1). Same force on a smaller area (1) gives a higher pressure at the point, so it pushes into the ground (1). [3 marks]
Question 3
The larger the contact area, the shallower the print (1). Jess's weight, 500 N, stayed the same (1). [2 marks]
Question 4
Deeper than 16 mm (1). The same 500 N on a smaller area gives a higher pressure (1). [2 marks]
Question 5
Marking guide: 1 the elephant is about 50 times heavier, so it pushes down with a much bigger force; 1 its four feet spread that force over a large area, about 2000 cm²; 1 the heel tip is tiny, about 1 cm²; 1 pressure depends on force and area, not force alone; 1 conclusion: the person's smaller force is concentrated on a far smaller area, so the pressure is higher. [5 marks]
Model answer: The elephant pushes down with a much bigger force, but spreads it over about 2000 cm². The person's smaller force is concentrated on a heel tip of about 1 cm². Pressure depends on force and area, so the tiny area gives the person the higher pressure.
Common error: thinking the heavier object always makes more pressure.