Year 9 Science — Pressure and how it is shared
Work out pressure from a force and an area, and explain why the same force presses harder when it is spread over less of a surface.
Name: ________________________
1.Why is a household water tank put up on the roof rather than at ground level?
- a) A tank on the roof holds more water than the same tank on the ground
- b) Water becomes heavier when it is higher up
- c) A taller column of water raises the pressure at the taps, giving a better stream
- d) Water flows faster in a warm tank than a cool one
2.A wooden block rests on a table, pressing down with a force of 60 N over an area of 4 m². What is the pressure, in N/m²? Answer with a number.
3.Each of these is a way of choosing how much surface a force lands on. Sort them by the pressure that follows.
Groups: High pressure · Low pressure
- The pointed end of a nail
- A broad shoulder strap
- The sharp edge of a knife
- The broad base of a dam
4.The air above a patch of skin 15 cm by 15 cm presses down with about the same force as gravity on a 225 kg object. Why does that not crush us?
- a) Air is so light that it cannot really press on anything
- b) The air pushes upwards as much as it pushes downwards, so it cancels out
- c) The pressure inside our bodies is equal to it and balances it
- d) Our skin is too tough for air to press through
5.Match each thing you can watch happen to what it tells you about pressure.
- Water spurts from holes made in the sides of a filled bottle
- Balloons on two pipes of different widths, filled to the same level, bulge the same amount
- A rubber sucker pressed onto smooth tiles will not pull off easily
- A paper plate is harder to lift under an unfolded sheet than a folded one
- it is the height of the water column that sets the pressure, not the width
- the air outside it presses harder than the thinned-out air trapped inside
- a liquid presses on the sides of its container too, not just the bottom
- air pushes with a bigger force when it has a bigger area to push on
6.The pressure exerted by the air around us has a two-word name in the chapter. What is it?
7.A crate pushes down on a floor with a force of 900 N, spread over an area of 3 m². What is the pressure on the floor, in N/m²? Answer with a number.
8.Holes are made low down in the sides of a bottle full of water, and the tape sealing them is pulled off. What happens, and what does it show?
- a) Air rushes in through the holes, showing that liquids press outwards less than air presses inwards
- b) Nothing flows out, showing that a liquid presses downwards and not sideways
- c) Water flows out sideways, showing that a liquid presses on the sides of its container as well as the bottom
- d) Water flows out sideways, showing that liquids press hardest at the top of the container
Answer key — Year 9 Science — Pressure and how it is shared
- 1. c) A taller column of water raises the pressure at the taps, giving a better stream
- 2. 15
- 3. The pointed end of a nail → High pressure; The sharp edge of a knife → High pressure; A broad shoulder strap → Low pressure; The broad base of a dam → Low pressure
- 4. c) The pressure inside our bodies is equal to it and balances it
- 5. Water spurts from holes made in the sides of a filled bottle → a liquid presses on the sides of its container too, not just the bottom; Balloons on two pipes of different widths, filled to the same level, bulge the same amount → it is the height of the water column that sets the pressure, not the width; A rubber sucker pressed onto smooth tiles will not pull off easily → the air outside it presses harder than the thinned-out air trapped inside; A paper plate is harder to lift under an unfolded sheet than a folded one → air pushes with a bigger force when it has a bigger area to push on
- 6. atmospheric pressure
- 7. 300
- 8. c) Water flows out sideways, showing that a liquid presses on the sides of its container as well as the bottom