Work, Energy and Momentum

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Whenever a force is applied to an object, it causes it to move. When a force moves an object, energy is transferred and work is done.  When work is done moving the object, the supplied energy is transferred to the object so the work done is equal to the energy transferred.  Both work and energy have the unit, joule.  The work done on an object can be calculated by using the equation:

W = F x d, where W= work done in J, F= force in N and d= distance moved in the direction of the force in m.

Work done to overcome friction is mainly transferred into energy by heating.  When the brakes are applied to a vehicle, friction between the brake pads and the wheel discs opposes the motion of the wheel.  The kinetic energy of the vehicle is transferred into energy that heats the brake pads and the wheel discs as well as the surrounding air.


Gravitational potential energy is energy stored in an object because of its position relative to the Earth's gravitational field.  Whenever an object is moved vertically upwards it gains gravitational potential energy equal to the work done on it by the lifting force.  Change in gravitational potential energy can be calculated by using the equation:

Ep = m x g x h, where Ep= change in gravitational potential energy in J, m= mass of the object in kg, g= graviational field strength in N/Kg and h= change in height in m.

Power is the rate of energy transfer. Power is calculated using the equation:

P = E/t, where P= power in W, E= energy transferrred in J and t= time for energy transfer in s.


All moving objects have kinetic energy.  The greater the mass and the faster the speed of an object, the more kinetic energy it has.  Kinetic energy is calculated by using the equation:

Ek = 1/2 x m x v2, where Ek=…


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