Pressure due to a column of liquid and atmospheric pressure: Forces: Physics: GCSE (9:1)

• Relationship between pressure in a liquid and depth

  Pressure increases as the depth of the fluid increases
• Cause of pressure in liquids

  The weight of the column of liquid above a surface
• p = hρg


  The equation linking pressure, height of the column, density of the liquid and gravitational field strength

  
• p


  The symbol for pressure

  
• h


  The symbol for height

  
• ρ (Greek letter rho)


  The symbol for density

  
• g

  The symbol for gravitational field strength

  
• Pascals (Pa)


  The SI unit for pressure

  
• Metres (m)


  The SI unit for height

  
• Kilograms per cubic metre (kg/m³)

  The SI unit for density
• Newtons per kilogram (N/kg)

  The SI unit for gravitational field strength
• Upthrust


  The resultant upwards force acting on an object that is partly, or completely, submerged in liquid

  
• Cause of upthrust


  There is more pressure acting on the bottom surface of a submerged object than on its top surface

  
• When do objects sink

  When the upthrust acting on the object is less than the weight of the object
• When do objects float

  When the upthrust acting on the object is larger than the weight of the object
• Atmospheric pressure


  Caused by air molecules in the atmosphere colliding with a surface

  
• Relationship between atmospheric pressure and height above ground level

  Atmospheric pressure decreases as the height of a surface above ground level increases

  
• Reason why atmospheric pressure decreases with height

  The number of air molecules (and so the weight of air) above a surface decreases as the height above ground level increases