momentum

• conservation of momentum

  • momentum can’t be created nor destroyed
  • sum of momentum before collision = sim of momentum after collision
• change in momentum = mv-mu

  where u is the initial velocity and v is the final velocity
• force = change in momentum / time
• using ideas about momentum, describe how a rocket is launched:

  • rocket starts at rest and has no momentum
  • rocket pushes fuel out of bottom of rocket
  • fuel has gained momentum in the direction of the ground (earth)
  • conservation of momentum means the rest of the rocket must gain momentum in opposite direction which propels the rocket into sky
• • if an object which has a lot of momentum is made to stop suddenly, then a large force is required because of the change in momentum
• safety features in car:

  • seat belts
  • crumple zones
  • air bags
• how do safety features in cars work?

  • they increase the time taken for the change in momentum to happen, which reduces the forces involved
• how do crumple zones work?

  • increase time taken for a change in momentum to take place
  • reduces the force experienced by driver
• how do safety features in a car reduce the force felt by a person in a crash?

  • when a crash takes place, there’s a certain change in momentum
  • the force felt by the person is the change in momentum divided by the time taken
  • safety features of a car increase the time taken for the momentum to change
  • therefore reducing force felt by person in crash