Energy Revision

Energy is the ability to do "work".  Which means that it is what makes everything around us happen.  There are different types of energy.  We have been looking at some of the different types of energy and how energy can be transferred from one form to another.  This is a quick revision guide to what we have been doing in class.

Generally energy (or work done) can be found by multiplying the force by the distance it was exerted over, using the equation:
               E (wd) = F d (s)

Power is the rate at which energy is converted. This is another general energy question you need to be aware of. So power is the energy converted over time, or energy is power multiplied by time.
               E = Pt

Potential Energy is the energy a body possesses when it is positioned above the ground (datum) level, it is dependent on the weight (mass x g) x height:
               Ep = mgh

G is the acceleration due to gravity, so the rate at which we are being pulled towards earth.  It is a constant at 9.81 m/s/s on earth.


Kinetic Energy is movement energy.  The greater the mass and speed of a boy, the greater the kinetic energy.
             Ek = 1/2 mv2

Thermal Energy is heat energy.
             Eh = cmΔt 

C is the specific heat capacity of a material and it is constant.  For water C = 4190 J/KgK

Electrical Energy is based on the equations for electrical power, and the general energy power equation.
              E = Pt             P = VI    Therefore  Ee = VIt

Strain energy is the energy generated by stretching or compressing a spring.  First of all you may need to find the force required by multiplying the spring stiffness, in Newtons per millimetre, by the extension or compression.  This will give you the total force to use in the equation:

           Es = 1/2 Fx

Remember that although you need to use millimetres to find the force, x is measured in metres.

To find the efficiency of a system you must look at the energy in and the useful energy out.  Some energy will be "lost" i.e. the heat energy produced by a light bulb, or heat energy produced by friction in moving parts.
            n = Output Energy/Input Energy   (to make it a percentage, multiply by 100.