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Forces and Matter

Pressure in liquids: density and depth

  • 3 things to know
  • Paper 2

Overview

Why liquid pressure rises with depth and density but not with container width, jets from holes at different heights, divers in sea and fresh water, pressure = height × density × gravitational field strength with calculations, and adding atmospheric pressure.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Key term

Explain why the pressure in a liquid increases with depth.

Key term

Explain why the pressure at a given depth is greater in a denser liquid.

Key term

Explain why the pressure at a point in a liquid does not depend on how wide the container is.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Explain why the pressure in a liquid increases with depth.

    Model answer

    The deeper the point, the greater the weight of liquid above each square metre pressing down on it.

  2. 2

    Explain why the pressure at a given depth is greater in a denser liquid.

    Model answer

    A denser liquid has more mass in each cubic metre, so the column of liquid above the point weighs more.

  3. 3

    Explain why the pressure at a point in a liquid does not depend on how wide the container is.

    Model answer

    The pressure depends on the height of liquid above the point, not on how much liquid lies beside it.

  4. 4

    A tall container of water has identical holes at three different heights. Explain why water squirts out fastest from the lowest hole.

    Model answer

    The pressure is greatest at the greatest depth, so the water is pushed out fastest there.

  5. 5

    Explain why the pressure at the base of a narrow tube holding water 2 m tall equals the pressure at the base of a wide tank of water 2 m deep.

    Model answer

    Both have the same height of liquid of the same density above the base.

  6. 6

    Explain why a diver 10 m below the surface of the sea experiences a greater pressure than a diver 10 m below the surface of a freshwater lake.

    Model answer

    Sea water is denser, so the column of liquid above the diver weighs more.

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