work and energy

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Cards (13)

  • when a force acts on a body work is done. work is a measure of the energy transferred. it is always measured in joules.
  • work= force x distance moved
  • when work is done, the total energy in the system must stay the same. the total energy at the start must equal the total energy at the end of the action. however, the energy may have changed from one kind to another.
  • kinetic energy= mass x velocity2^2/2
  • gravitational potential energy= mass x gravitational field strength x change in height
  • energy stored in a spring = the area under the force extension graph
  • linear graph:
    w=1/2fx where f is force and x is extension
  • putting force on a spring will cause it to stretch. the amount it will stretch, the extension. for a given force depends on the spring itself. each spring will have a different spring constant which will determine how much force is required to stretch a spring.
  • spring constant equation:
    force= spring constant x extension
  • in most cases the transfer of energy is not efficient. some energy is lost due to the work done by friction.
  • car efficiency:
    the efficiency of cars in an important area of development. cars are being made more efficient in order to reduce greenhouse gases and waste less energy.
  • reducing losses in cars:
    • start-stop systems to reduce waste whilst stationary.
    • lighter materials to reduce the mass of the car.
    • more streamlined shapes to reduce the work done by frictional forces on the car.
    • ensuring correctly inflated tyres to reduce the work done by frictional forces (often done by using a sensor to alert the driver if the tyres are not correctly inflated).
  • car safety features:
    modern cars have built in features to reduce the forces acting on passengers in a collision. these include airbags and crumple zones. these features both change shape during a collision, this allows the work to reduce the kinetic energy of the passengers to be done over a long distance. the longer the distance the work is done over, the smaller the force on the passengers will be.