“Energy – is the ability or capacity to do work”
“Work is – moving something against a force”
“Energy cannot be created or destroyed”, energy can only be transformed or converted”.
(The first law of thermodynamics)
Forms of energy
Energy can be converted or transformed from one form of energy into other forms of energy in three basic ways
1.Through the action of forces, which has several cases:
Gravitational Forces – When gravity accelerates a falling object, its converts its potential energy to kinetic energy. Likewise, when an object is lifted the gravitational field stores the energy exerted by the lifter on the object as potential energy.
Electric and magnetic force fields – Charged particles that are influenced by forces from electrical or magnetic fields possess potential energy in a way similar to that of an object in a gravitational field.
These force fields can accelerate the particles, converting the particle’s potential energy into kinetic energy. Also charged particles can interact via the electric and magnetic fields they create, transferring energy between them, causing molecules to vibrate such that the electrical potential energy is converted into heat.
Frictional Forces – The potential and kinetic energy of an object, which is associated with the position, orientation, or motion of the entire object can be converted into thermal energy (heat), if the object slides against another object or matter. The sliding causes the molecules on the surfaces of contact to interact via electromagnetic fields with one another and start vibrating and generating heat
2. When atoms absorb or emit photons of light.
Absorption of light – When light falls on an object, an incident photon may either pass through the object, be reflected by the object, or be absorbed by the atoms making up the object.
If most of the photons pass through, the object is said to be transparent. Depending on the smoothness of the surface and on the scale of the photon’s wavelength, the reflection may be either diffuse (rough surface) or coherent (smooth surface).
If the photon is absorbed, the photon’s energy may also be split up and converted in the following ways:
Photo thermal effect – Is when the energy absorbed simply produces thermal energy, or heat in the object. In this case the photon’s energy is converted into vibrations of the molecules called phonons, which is actually heat energy.
Photoelectric effect – Is when the energy absorbed is converted into kinetic energy of conduction electrons, and hence electrical energy.
An example is photovoltaic cells (solar cells) that convert the energy of the sunlight directly into electrical energy.
Photochemical effect – Is when the energy brings about chemical changes, which stores the energy.
An example is the photosynthesis of green plants that converts the energy of the sunlight into chemical energy (carbohydrates).
3. Nuclear reactions.
Nuclear reactions – When there are rearrangements of the subatomic particles that make up the nuclei of atoms and nuclear reactions occur.
There are two basic types of nuclear reactions:
Fission – When nuclei split apart.
Fusion – When nuclei combine.