Pressure in a liquid

• Factors Affecting Pressure in a Liquid

  • When an object is immersed in a liquid, the liquid will exert a pressure evenly across the whole surface of the liquid and in all directions
  • Greater the depth or density = greater the pressure
  • In a liquid, the pressure  increases with the height of the column.
  • More liquid above = more pressure
  • This is because the pressure in a liquid is caused by the weight of the liquid
  • As the liquid becomes deeper, the amount of liquid and weight causes the pressure to increase
  • The pressure on the seabed is higher than at the surface of the ocean
• Pressure in liquid

  A) Low

  B) High

  C) Strongest

  D) Weakest

  
• • 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
• Pressure Differences & Upthrust

  • Upthrust is due to the difference in pressure between the top and the bottom of the submerged object
  • A partially (or totally) submerged object experiences a greater pressure on the bottom surface than on the top surface
  • This is because the pressure p is proportional to the depth h of the object
  • The difference in pressure creates a resultant force upwards (upthrust)
  • Upthrust is why objects appear to weigh less when immersed in a liquid
• • The amount of upthrust on an object depends on the weight of the fluid that the object displaces
  • Upthrust is equal to the weight of fluid displaced
• Calculating Pressure in a Liquid

  • The pressure due to a column of liquid can be calculated using the equation

  p = h × ρ × g

  • p = pressure in pascals (Pa)
  • h = height of the column in metres (m)
  • ρ = density of the liquid in kilograms per metre cubed (kg/m3)
  • g = gravitational field strength on Earth in newtons per kilogram (N/kg)
  • The force from the pressure is exerted evenly across the whole surface of an object in a liquid, and in all directions
• The force from the pressure of objects in a liquid is exerted evenly across its whole surface

  • The pressure is more accurately a difference in pressure at different depths h in a liquid, since the pressure changes with the depth