Energy and work are both measured in joules (J).
Power is measured in watts (W).
Kinetic energy is energy of motion. Any object which is in motion (moving) has kinetic energy.
Potential energy is stored energy, or energy that is ready to be used. Objects can have
potential energy because of a force acting upon them. For example:
-
An apple held up in the air has potential energy because of the force of gravity acting
downwards on it. If the apple is let go, the Earth’s gravitational field will act upon it, and
it will fall to the ground.
This is an example of potential energy (the apple being held up in the air against the
force of gravity) turning to kinetic energy (the apple falling towards the ground).
Potential energy due to gravity is called gravitational potential energy.
FORMULAS:
KINETIC ENERGY =
MASS * VELOCITY
2
2
= (m*v2)/2
GRAVITATIONAL POTENTIAL ENERGY = mass * gravitational constant * height = mgh
NOTE: For the kinetic energy formula, the mass is to be given in kilograms and the velocity in
metres per second. Therefore, if a question to do with kinetic energy gives the mass of an
object in grams, convert this into kilograms before inputting the value into the formula.
NOTE: For the gravitational potential energy formula, the mass is to be given in kilograms, the
gravitational constant in Newtons per kilogram and the height in metres.
Both kinetic and potential energy is measured in joules (J).
A question on gravitational potential energy can be found here, starting on page 12.
DIFFERENT TYPES OF ENERGY
KINETIC ENERGY
POTENTIAL ENERGY
THERMAL ENERGY
CHEMICAL ENERGY
ELECTRICAL ENERGY
NUCLEAR ENERGY
SOUND ENERGY
LIGHT ENERGY
The energy of motion. A ball flying through the air has kinetic energy. An
object has kinetic energy if it can do work on another object if it collides
with it. For example, if the ball hits a cone, it will cause the cone to move
or fall over. Thus, we can see that the ball has kinetic energy.
Stored energy. A book sitting on a shelf has potential energy because if it
falls off, the force of gravity will act upon it, making it accelerate towards
the ground.
Heat energy. A cup of hot water has thermal energy because the
molecules of water are vibrating and moving.
For example: glucose has chemical energy because it releases energy
when it combusts (reacts with oxygen). Crude oil also has chemical
energy.
Energy stored in an electric field or transported by an electric current.
For example: the energy stored in the coils of an electrical generator in a
power station.
The atoms in a radioactive element such as uranium can be split by firing
neutrons at them. This splitting process releases great amounts of
energy.
Also, the nuclei of atoms can be fused together under very hot
conditions (such as in the sun or other stars), which also releases great
amounts of energy.
Sound waves are compression waves. When a sound is made, for
example by a large drum, the air near the drum is compressed, giving it
potential energy. The air then expands, transforming the potential
energy into kinetic energy. This moving air has the same effect on the air
near it, making it compress and then expand, and the air near that
compresses and then expands, etc.
Light is a form of electromagnetic radiation. Electromagnetic waves
contain photons which move at the speed of light. Each photon contains
a certain amount of energy. If light is absorbed, the photons transfer
their energy to the atoms absorbing the light.
Examples of light energy can be found in candles, flashlights, stars, lightbulbs and fire.
Energy cannot be created or destroyed, but it can be converted to different forms:
The chemical energy in a battery is converted to light energy in a bulb.
Light energy is converted to chemical energy in a solar panel.
The chemical energy in a cyclist’s body is converted to kinetic energy in the bike.
The sound energy in someone’s voice can be converted to electrical energy in a microphone,
and then back to sound energy in a loudspeaker.