pressure

• • pressure in liquid depends on depth and density
  • more dense, more particles able to collide, so higher pressure
  • as depth increases, number of particles increases
  • liquid pressure increases with deoth
  • formula = p g h
• • when object submerged in fluid, pressure exerts force in every direction
  • pressure increases with depth, so force exterted on bottom is large that force on top
  • creates resultant force upwards, this is upthrust
  • upthrust is equal to weight of fluid that has been displaced by object
• • if upthrust is equal to object's weight, forces balance and object floats
  • if weight is more than upthrust, object sinks
  • less dense object than fluid weighs less than equivalent volume of fluid
  • displaces volue of fluid
  • more dense object than fuid unable to displace fluid to equal weight
  • weight larger than upthrust so it sinks
• • to sink submarines, large tanks filled with water to increase weight of submarine so is more than upthrust
  • to float, tanks filled with compressed air to reduce weight so is less than upthrust
• • atmosphere thin compared to Earth
  • atmosphere becomes less dense as altitude increases
  • air molecules collding with surface area causes atmospheric pressure
  • atmospheric pressure decreases as height of surface increases
  • as altitude increases:
  • number of air molecules decreases
  • weight of air decreases
  • less air above surface
• • aircrafts that fly at high altitudes must be pressurised
  • if air pressure is low, humans cannot take in oxygen quickly enough for respiration