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Physics · Grades 7–10

Pressure, area and depth

Do not confuse pressure with force or absolute with additional pressure.

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Learn the idea

Surface pressure

Uniform pressure equals normal force divided by area. Convert area units carefully.

Liquid depth

In a uniform liquid, pressure rises with depth by density times g times depth.

Surface baseline

The depth formula gives an increase relative to the surface. Add surface pressure when absolute pressure is requested.

Compare fairly

At the same force, a smaller contact area produces greater average pressure.

Worked examples

A 40 N normal force acts over 0.2 m². Find average pressure.

40/0.2 = 200 Pa.

200 Pa

At the same normal force, halving area does what to pressure?

Pressure is inversely proportional to area at fixed force.

Doubles it

Check your understanding

  1. A liquid has density 1000 kg/m³. At depth 2 m, with g = 10 m/s², find pressure above surface pressure.

  2. Surface pressure is 100000 Pa and the liquid adds 15000 Pa. Find absolute pressure.

  3. Which quantity is measured in pascals?

    1. Force
    2. Pressure
    3. Energy

Answers and marking notes

Answers and marking notes
  1. 20000 Pa

    ρgh = 1000 × 10 × 2 = 20000 Pa.

  2. 115000 Pa

    Add baseline and increase: 100000 + 15000.

  3. Pressure

    One pascal is one newton per square metre.

Further reading and review references

These are reference links, not copied exercises, institutional endorsement or proof of independent review.

Independent educational review required. Grade bands are approximate; these are not officially aligned curricula.