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      Pressure at different depths and heights

      Lesson details

      Learning outcome

      I can describe how the pressure changes at different depths underwater and heights in the atmosphere.

      Key learning points

      1. The bigger the surface area of a boat’s hull, the bigger the upthrust on it can be.
      2. Pressure in liquid increases with depth because there is more liquid pushing down.
      3. 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.

      Teacher tip

      Performing a live 'can crushing' experiment with a vacuum pump (or cooling steam) will make the lessons much more dramatic.

      Licence

      This content is © Oak National Academy Limited (2026), 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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      Prior knowledge starter quiz

      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
      decreasing the force used
      Correct answer: 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

      Q3.
      Which of these is the correct equation to calculate pressure?

      $$ pressure = {force \times area}$$
      Correct answer: $$ pressure = {force \over area}$$
      $$ pressure = {force + area}$$
      $$ pressure = {force - area}$$

      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$$^2$$
      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

      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 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$$^2$$

      6 Questions

      Q1.
      Match the key words and phrases to the explanations.

      Correct Answer:upthrust,a force acting upwards due to pressure differences

      a force acting upwards due to pressure differences

      Correct Answer:pressure,the effect of a force acting over an area

      the effect of a force acting over an area

      Correct Answer:depth,the distance under the surface of a liquid

      the distance under the surface of a liquid

      Correct Answer:atmospheric pressure,the pressure caused by the air in the atmosphere

      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
      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$$^2$$
      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?

      An image in a quiz
      the pressure decreases with depth
      Correct answer: the pressure increases with depth
      Correct answer: 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
      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)
      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

      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.
      The card is waterproof so the water cannot escape.

      To help you plan your 9 science lesson on: Pressure at different depths and heights, download all teaching resources for free and adapt to suit your pupils' needs...