Physics P3 Crumple Zones

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  • Created by: A.P
  • Created on: 20-01-13 14:27
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  • Crumple Zones
    • Momentum and Force
      • Momentum = Mass x Velocity
        • Momentum is measured in kgm/s
      • To reduce injuries in a collision, forces should be as small as possible.
        • Force = Change in Momentum / Time
        • Spreading the momentum change over a longer time reduces the force.
          • To minimise injury, forces acting on the people in a cur during an accident must be minimised.
            • Force = Mass x Acceleration
      • Force can be reduced by reducing the acceleration. This can be done by...
        • ...increasing stopping or collision time.
        • ...increasing stopping or collision distance.
        • Safety features that do this include crumple zones, seat belts, air bags, crash barriers and escape lanes.
    • Car Safety Features
      • Modern cars have safety features that absorb energy when a vehicle stops suddenly. These are:
        • Brakes that get hot.
        • Crumple zones that change shape.
          • On impact the crumple zones at the front and rear of the car absorb some oof its energy by changing shape or 'crumpling'.
        • Seat belts that stretch a little.
          • On impact they stretch slightly so that some of the person's kinetic energy is converted to elastic energy.
        • Air bags that inflate and squash.
          • On impact they absorb some of the person's kinetic energy by squashing up around them.
      • All of these features absorb energy and range shape to reduce injuries. They reduce the momentum to zero slowly, therefore reducing the force on the occupants.
      • Some people don't like wearing seatbelts because...
        • ...there is an increased risk of chest injury.
        • ...they may be trapped in a fire.
        • ...drivers may be encourages to drive less carefully because they know they have the protection from a seat belt.
      • Despite computer modelling, crash tests using real vehicles and dummies provide more safety information.
      • ABS brakes are a primary safety feature which helps to prevent a crash.
        • In the ABS system, wheel-speed sensors send information to a computer about the rotational speed of the wheels. The computer controls the pressure to the brakes, via a pump, to prevent the wheels locking up. This increases the braking force (F) just before the wheels start to skid.
          • Kinetic Energy Lost = Work Done by the Brakes
          • 1/2 x m x (v squared) = F x d where m = mass of car, v = speed of car before braking, d = braking distance. If F increases the braking distance decreases.
        • Other primary safety features include...
          • control which stops a driver becoming tired on a long hourney and pressing harder on the accelerator.
          • ...electric windows and paddle shift controls which allow the driver to concentrate on the road.


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