Conservation of Energy
The Law of Conservation of Energy States:
Energy is neither created nor destroyed; it is converted from one form to another.
The above nonsense (including spelling mistake) is reproduced from a student's answer in a test!
At GCSE you would have done some energy chains, for example in a nuclear power station.
Nuclear energy is converted into heat.
Heat boils water to steam
Heat in the steam is converted into kinetic energy in the turbines
Which is converted into electrical energy in the generator.
Potential Energy
This term is often used in the
context of gravitational potential energy.
If we lift an object of mass m
against gravity, we are doing a job of work.
Work done = PE = weight × distance moved against gravity.
Notice the term Dh ("delta h"). This means "change in height". So if we lifted an object from 200 m above sea level to 300 m above sea level, the change in height is 100 metres, which we would use in the equation.
Watch out for the bear trap of
using weight in kilograms.
| What is the potential energy of a 12 kg mass raised from the ground to a to a height of 25 m? |
Kinetic Energy
Kinetic energy is the ability to do work through motion. If the motion is in a straight line, we call the kinetic energy translational. This is the only kinetic energy we will consider.
| Calculate the kinetic energy of a 4 kg shot-put thrown by an athlete at a speed of 15 m/s. |
If an object falls, the potential energy is turned into kinetic energy. Then we combine the equations for Ep and Ek, (conservation of energy):
Ep = Ek,
mgDh = ½ mv2
mgDh = ½ mv2
Þ v2 = 2gDh
| A coin is dropped from the viewing platform of an observation tower 80 m high. How fast will it travel just before it hits the ground? Why don't you need to know the mass? |
| Now try Topic Test | Home | Unit 2 | Physics AS |