Fluid Pressure

• Pressure


  Force per Unit Area
• Fluids


  • Substances that can 'flow' because their particles are able to move around
  • Particles collide with surfaces and other particles
  • Particles have mass and exert a force on the object they collide with
• Pressure in a fluid

  A force is exerted normal (at right angles) to any surface in contact with the fluid
• Calculating pressure at the surface of a fluid

  1. F/A

  2. F = Force normal to a surface (N)

  3. A = Area of that surface (m²)
• Fluid


  Either a liquid or gas
• Pressure in a Liquid

  • Depends on depth and density
  • Density is a measure of the 'compactness' of a substance, i.e. how close together the particles in a substance are
  • The more dense a given liquid is, the more particles it has in a certain space, so the pressure is higher
  • As the depth of the liquid increases, the number of particles above that point increases, so the weight of these particles adds to the pressure felt at that point
• Calculating pressure at a certain depth due to the column of liquid above


  1. p = hρg

  2. p = Pressure (Pa)

  3. h = Height of the column of liquid (the depth) (m)

  4. ρ = Density of the liquid (kg/m³)

  5. g = Gravitational field strength (N/kg)
• Calculating change in pressure between 25 m and 45 m depth in water

  • Pressure at 25 m = 245,000 Pa
  • Pressure at 45 m = 441,000 Pa
  • Change in pressure = 441,000 - 245,000 = 196,000 Pa
• Standard form


  A x 10^n, where A is a number between 1 and 10, and n is the number of places the decimal point would move if you wrote the number out fully (negative for numbers less than 1, positive for numbers greater than 1)