P2.2

P2.2

1. Forces and Energy

   • When a force causes an object to move through a distance work is done
   • Work done, force and distance are related by the equation: W = F x d
     • W is work done joules, F is force applied in N, d is the distance moved in the direction of the force in m
     • Work done against frictional forces is mainly transferred into heat energy.
       • For an object that is able to recover its original shape, elastic potential energy is the energy stored in the object when work is done to change its shape.

2. Power is the work done or energy transferred in a given time

   • P = E/t
     • P = Power in Watts (W), E is the energy transferred in joules (J), t is the time taken in seconds (s)

3. Gravitational Potential energy is the energy that an object has by virtue of its position in a gravitational field

   • Ep = m x g x h
     • Ep is the change in gravitational potential energy in J, m is the mass in kg, g is the gravitational field strength in N/kg, h is the change in height in m
   • When an object is lifted, work is done against the force of gravity and the object gains gravitational potential energy
   • The kinetic energy of an object depends on its mass and speed
     • Ek = 1/2 x m x v squared
       • Ek is kinetic energy (j), m is mass in kg, v is speed in m/s

4. Momentum

   • Momentum is a property of moving objects
     • p = m x v
       • p is momentum (kg m/s), m is mass (kg), v is velocity (m/s)
   • In a closed system the total momentum before an event (collisions or explosions) is qual to the total momentum after the event. This is called the conservation of momentum