pressure and pressure differences

• a fluid can either be a liquid or gas
• if pressure acts on a bigger area is will produce a larger force
• the atmosphere is a relatively thin layer of air around the earth
• the greater the altitude the less dense the atmosphere and the lower the atmospheric pressure
• at a high altitude there is less air above a surface than at lower altitude so there is a smaller weight of air acting on the surface
• pressure in a column of liquid depends on

  • the height of the column above the point
  • the density of the liquid
• the higher the column the more dense the liquid

  • the greater weight above the point
  • the greater force on the surface at that point
  • the greater the pressure
• pressure of a liquid depends on the depth
• for an object to float , the upthrust must be equal to the objects weight
• if the upthrust is less than the objects weight it sinks
• size of the upthrust is the same as the weight of the water displaced
• if an bject can displace its own weight of water , then the upthrust will be equal to the objects weight and float