Liquid Pressure & Upthrust

This lesson covers:

  1. The equation for pressure in a liquid: p=hρgp=hρg
  2. What the 'upthrust' force is

The factors which determine the pressure exerted by liquid are:


  1. The depth. At a greater depth, more pressure is exerted.
  2. The density of the liquid. More dense liquids exert greater pressure.
  3. The gravitational field strength, which is 9.8 N/m on earth. 

The formula for pressure in a liquid is:

p=mg
p=ρhg​
p=hρg

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What are the units of pressure in a liquid?

Kilograms (kg)

Newtons (N)

Pascals (Pa)

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The density of water is 1000 kg/m3. The Earth's gravitational field strength is 9.8 N/m.


Calculate the pressure at a depth of 3 m in water.

29400

Pa

Pa

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The density of water is 1000 kg/m3. The Earth's gravitational field strength is 9.8 N/m.


What is the depth that would have a pressure of 39,200 Pa in water?

4

m

m

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Illustration showing a cube causing a water splash, demonstrating upthrust.

Upthrust is caused by:

The pressure on the bottom of the object being greater than the pressure on the top of the object

The object pushing the Earth's magnetic field

The object not being affected by gravity whilst under water

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Objects which are more dense than the liquid they are in will _________.

sink

float

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