Work, Energy and Momentum

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  • Work, Energy and Momentum
    • Energy and Work
      • When work is done, the supplied energy is transferred to the object so the work done is equal to the energy transferred
      • W=F X D
        • Work done s measured in Joules
      • The work done to overcome friction is transferred into energy by heating
    • Gravitational Potential Energy
      • Energy stored in an object due to its position on Earth's gravitational field
      • Ep=m x g x h
      • Power is the rate of transfer energy
        • P= E/T
        • Power- Watts (W)
    • Kinetic Energy
      • The greater the mass the faster the speed of the object- the more kinetic energy it has
      • Energy in elastic once being stretched is called Elastic Potential Energy
        • When the elastic returns to its original shape the energy is released
    • Momentum
      • All moving objects have momentum
      • The greater the mass the greater velocity of an object- the greater its momentum
      • p= m x v
      • Law of conservation of Momentum
        • The total change in momentum is zero
        • The total momentum before is equal to the total momentum after
    • Explosions
      • In and explosion the objects move apart with equal and opposite momentum
        • One direction must be defined as positive and the opposite must be defined negative
        • So the total momentum after the explosion is zero
    • Impact forces
      • When a force acts on a moving object, its momentum changes
      • The longer the time taken for change in momentum, the smaller the force then acts
      • If the impact time is short, the force is large. As impact time increases the forces become less
      • Crumple zones- e.g. cars folding in on themselves increases the impact time so reduces the force on the car

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