Physics P2 Revision

Physics P2 Revision

1. Force and energy

   • When a force acts upon an object causing it to move through a distance energy is transferred and work is done. The amount of work done is equal to the amount of energy transferred.
     • Work done (J) = Force applied (N) * distance moved (m)
   • If you try to do work against a surface with friction then most of the energy gets transformed into heat.
   • Power is the amount of work done (energy transferred) every second.
     • Power (W) = Energy transformed (J) / time (s)
   • Work can also be done on other objects. If you change the shape of an object then the energy gets stored in the object, e.g. an elastic band.
     • This is elastic potential energy. Remember, the potential energy is stored energy that is 'waiting' to be used, kinetic energy is movement energy.
   • Gravitational potential energy is the amount of energy an object has when it is held above the ground.
     • Gravitational potential energy (J) = mass (kg) * gravitational field (N/kg) * height (m)
   • To work out the kinetic energy a body has you need to know it's mass and it's velocity; Kinetic energy (J) = half * mass (kg) * velocity(squared) (m/s(squared))

2. Momentum

   • Momentum (has the symbol p) describes how much motion an object has. It is measured in kilogram meter per second (kg m/s). Like velocity, momentum has magnitude acting in a certain direction.
     • Momentum (kg m/s) = Mass (kg) * Velocity (m/s)
   • In all situations, momentum is conserved, providing there are no external forces acting. For collisions, the momentum before the collision is equal to the momentum after the collision e.g. snooker balls.