P11 forces and pressure

• large area = small pressure
• small area = large pressure
• pressure = force / area
• gas pressure is caused by particles colliding with each other and the walls of the container
• gas particles exert a force on it's container walls when they collide
• in a liquid particles are closer together and cannot be squashed
• pressure in a liquid is transmitted through the fluid
• the deeper a fluid is the greater the pressure
• the pressure in a liquid is the same if the depth is the same
• pressure = density x height x gravitational field
• upthrust acts upwards because the pressure at the bottom of the object is greater than at the top so it is the resultant force
• the more the object is lowered, the more water is displaced therefore increasing the upthrust
• the maximum upthrust is equal to the weight of the water displaced
• an object floats when its weight is equal to the upthrust
• in order to float in a liquid with a low density, a higher volume of water needs to be displaced
• an objects sinks when it's weight is greater than the upthrust
• pressure is caused when an object exerts forces on each other
• the pressure in a liquid increases with depth
• the pressure of a liquid depends on the density of a liquid
• conservation of momentum


  in a closed system the total momentum before an event is equal to the total momentum after the event
• safety features

  • increase time taken for collision
  • decrease rate of change of collision
  • reduce the force
  • less likely to be injured
• safety features on car

  • front crumply zone
  • seat belt
  • airbag
  • rear crumple zone
• objects which are stretched or squashed store elastic potential energy
• an elastic object will return to it's original shape when the force is removed
• if an object returns to it's original shape after the force is removed, it obeys Hooke's law