Work, energy and momentum - key points

Work, energy and momentum - key points

1. Energy and work

   • Work is done on an object when a force makes the object move
   • Work done to overcome friction is transferred as energy that heats the objects that rub together and the surroundings
   • Energy transferred =
     • Word done
   • Work done (joules) =
     • force (newtons) x distance moved in the direction of the force (metres)

2. Kinetic energy

   • The kinetic energy of a moving object depends on its mass and its speed
   • Elastic potential energy is the energy stored in an elastic object when work is done on the object
   • Kinetic energy (J) =
     • 1/2 x mass(kg) x speed(m/s/s)

3. Gravitational potential energy

   • The gravitational potential energy of an object depends on its weight and how far it moves vertically
   • The change of gravitational potential energy of an object is equal to its mass x the gravitational field strenght x its change of height
   • The gravitational potential energy of an object increases when the object goes up and decreases when the object goes down

4. Momentum

   • Momentum =
     • mass x velocity
   • The unit of momentum is kg m/s
   • Momentum is conserved whenever objects interact, provided the objects are in a closed system so that no external forces act on them.

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