New
New
Year 9
Pressure at different depths and heights
I can describe how the pressure changes at different depths underwater and heights in the atmosphere.
New
New
Year 9
Pressure at different depths and heights
I can describe how the pressure changes at different depths underwater and heights in the atmosphere.
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Lesson details
Key learning points
- The bigger the surface area of a boat’s hull, the bigger the upthrust on it can be.
- Pressure in liquid increases with depth because there is more liquid pushing down.
- Pressure in the atmosphere reduces with height because there is less air pushing down.
Keywords
Upthrust - A force acting upwards due to pressure is an upthrust.
Pressure - The pressure on a surface is the effect of a force acting over an area.
Depth - Depth is the distance under the surface of a liquid.
Atmospheric pressure - Atmospheric pressure is the pressure caused by the atmosphere, this decreases with height.
Common misconception
Pressure is greater at the bottom of a wider container than at the bottom of a narrower one.
Discuss how the force of water in the wider container is acting over a bigger area and refer to pressure = force ÷ area.
Performing a live 'can crushing' experiment with a vacuum pump (or cooling steam) will make the lessons much more dramatic.
Teacher tip
Content guidance
- Risk assessment required - equipment
Supervision
Adult supervision required
Licence
This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).
Lesson video
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Starter quiz
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6 Questions
Q1.
Which of the following will increase the pressure produced by a knife being used to cut a rope?
Correct answer: increasing the force used
increasing the force used
decreasing the force used
Correct answer: sharpening the knife to decrease the area of contact
sharpening the knife to decrease the area of contact
making the knife blunt to increase the area of contact
Q2.
A raft of weight 400 N floats on the surface of water. What is the size of the upthrust acting on the raft?
Correct Answer: 400 N, 400N, 400 newton, 400 newtons, 400 Newtons
400 N, 400N, 400 newton, 400 newtons, 400 Newtons
Q3.
Which of these is the correct equation to calculate pressure?
$$ pressure = {force \times area}$$
Correct answer: $$ pressure = {force \over area}$$
$$ pressure = {force \over area}$$
$$ pressure = {force + area}$$
$$ pressure = {force - area}$$
Q4.
A box with a weight of 30 N touches the floor over an area of 0.5 m$$^2$$. What pressure does the box produce on the floor?
29.5 N/m$$^2$$
30 N/m$$^2$$
30.5/m$$^2$$
Correct answer: 60 N/m$$^2$$
60 N/m$$^2$$
120 N/m$$^2$$
Q5.
A pupil pushes downwards with their hand which has a surface area of 60 cm$$^2$$. The pressure they produce is 1.2 N/cm$$^2$$. What sized force are they pushing down with?
50 N
60 N
61.2 N
Correct answer: 72 N
72 N
Q6.
Which of the following produces a pressure of one pascal (1 Pa)?
a force of 1 N acting over an area of 1 cm$$^2$$
a force of 1000 N acting over an area of 1 m$$^2$$
Correct answer: a force of 1 N acting over an area of 1 m$$^2$$
a force of 1 N acting over an area of 1 m$$^2$$
a force of 10 000 N acting over an area of 10 000 cm$$^2$$
Correct answer: a force of 1 N acting over an area of 10 000 cm$$^2$$
a force of 1 N acting over an area of 10 000 cm$$^2$$
Exit quiz
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6 Questions
Q1.
Match the key words and phrases to the explanations.
Correct Answer:upthrust,a force acting upwards due to pressure differences
upthrust -
a force acting upwards due to pressure differences
Correct Answer:pressure,the effect of a force acting over an area
pressure -
the effect of a force acting over an area
Correct Answer:depth,the distance under the surface of a liquid
depth -
the distance under the surface of a liquid
Correct Answer:atmospheric pressure,the pressure caused by the air in the atmosphere
atmospheric pressure -
the pressure caused by the air in the atmosphere
Q2.
Which of these will increase the maximum weight a raft can support before it starts to sink?
increasing the weight of the raft
decreasing the surface area of the raft
Correct answer: increasing the surface area of the raft
increasing the surface area of the raft
making the raft out of denser materials
Q3.
A raft of weight 2000 N and surface area of 4.0 m$$^2$$ floats on the surface of water. What pressure is the water putting on the raft?
0.002 N/m$$^2$$
Correct answer: 500 N/m$$^2$$
500 N/m$$^2$$
1996 N/m$$^2$$
2004 N/m$$^2$$
8000 N/m$$^2$$
Q4.
A shark is travelling deeper and deeper into the ocean. Which of the following are correct?
the pressure decreases with depth
Correct answer: the pressure increases with depth
the pressure increases with depth
Correct answer: the pressure acts from all directions
the pressure acts from all directions
the pressure acts only from above
Q5.
Sort these statements into order of the change in pressure. Start with the one describing the greatest change in pressure to the one describing the smallest change in pressure.
1 - moving from 1000 m under the surface of the ocean to 1000 m above it
1
- moving from 1000 m under the surface of the ocean to 1000 m above it
2 - moving from 100 m under the surface of the ocean to 1000 m above it
2
- moving from 100 m under the surface of the ocean to 1000 m above it
3 - moving from 100 m under the surface of the ocean to the surface (0 m)
3
- moving from 100 m under the surface of the ocean to the surface (0 m)
4 - moving from the surface of the ocean (0 m) to 1000 m above it
4
- moving from the surface of the ocean (0 m) to 1000 m above it
5 - moving from the surface of the ocean (0 m) to 100 m above it
5
- moving from the surface of the ocean (0 m) to 100 m above it
Q6.
A magician fills a glass with water and puts a sheet of card on top. They then turn the glass and card over carefully and the water does not fall out. What is the best explanation for this?
The water has become weightless as the card blocks gravitational forces.
The water pressure pushing down is about zero as the card has a very small area.
Correct answer: Air pressure below the card produces a force greater than the weight of water.
Air pressure below the card produces a force greater than the weight of water.
The card is waterproof so the water cannot escape.