Pressure in a Liquid (CIE IGCSE Physics)

Factors affecting pressure in a liquid

• The pressure beneath the surface of a liquid will increase with the depth of the liquid
  • This is because the pressure in a liquid is caused by the force of the weight of the liquid above it
  • As the depth increases, there is increasingly more liquid above which causes the pressure to increase
• Pressure in a liquid also depends on the density of the liquid
  • The more dense the liquid, the greater the pressure it exerts

Pressure in a column of water

• In a column of water, the highest pressure would be at the bottom
  • If a hole is made at the bottom of the column, the water will pour out with a large force
  • If a hole was made at the top of the column, the water will pour out with a small force
  • This is because of the difference in pressure in the column caused by the weight of the water

Extended tier only

• The pressure acting on an object in a liquid changes with depth
  • The deeper the object then the higher the pressure exerted upon it and vice versa
• The equation for the pressure difference, at different depths, in a liquid is given by the equation:

• Where:
  • Δp = change in pressure, measured in pascals (Pa)
    • Where 1 Pa = 1 N/m²
  • ρ = density of the liquid, measured in kilograms per metre cubed (kg/m³)
  • g = gravitational field strength on Earth, measured in newtons per kilogram (N/kg)
  • Δh = change in height of the column, measured in metres (m)

Pressure in a liquid with a density is applied at a depth 

The force from the pressure of objects in a liquid is exerted evenly across its whole surface