- Concepts of work and energy.
- Types of material systems with regards to the exchanges of energy and matter.
- Forms of energy: kinetic, gravitational potential, elastic potential, chemical, electric, nuclear, heat, light.
- Transfers and transformations of energy.
- Changes caused by transfers of energy; reversible and irreversible changes.
- Energy in human societies: foods, fossil fuels, nuclear, biomass, aeolian, hydraulic, solar.
- Types of power plants.
Forms of Energy
|Kinetic||It is the kind of energy that results from the movement of a body. The greater the speed and the mass of a body, the more the kinetic energy it has. It is a type of mechanical energy.|
|Gravitational potential||It is the kind of energy that results from the position of a body with regards to the centre of gravity of the planet (or other type of celestial body) it is in. The greater the altitude, the mass of the body and the mass of the planet, the more the gravitational potential energy it has. It is a type of mechanical energy.|
|Elastic potential||It is the kind of energy that results from the deformation of an elastic body. The greater the deformation, the more the tendency of the object to get back to its original shape, and so, the more the elastic potential energy it has. It is a type of mechanical energy.|
|Chemical||It is the kind of energy that makes up the chemical bonds in the molecules, this is, the kind of energy that keeps the atoms together in a molecule.|
|Electric||It is the kind of energy that shows up when the electrons of a group of atoms move in an specific direction, as in an electric current: the electrons of the copper threads move continuously from one end to the other.|
|Nuclear||Different to electrons, which are fairly easy to detach from their atoms, the protons and the neutrons of the nucleus of an atom are very difficult to separate. The nuclear energy is the kind of energy stored in those very powerful forces that keep together the particles of an atom's nucleus.|
|Light||Light, and the other types of electromagnetic radiations (infrared, ultraviolet, etc.), is a type of energy transmitted by waves.|
|Thermal||Or heat. It is a form of energy associated with the motion of atoms or molecules in a body: the quicker they move, the greater the amount of heat that that body contains. Heat shows up as a measurable property of the bodies: the temperature.|
Sources of Energy
|Foods||It is the kind of energy source that heterotroph living beings (or consumers) use. We use the chemical energy contained in the food molecules (the nutrients), and although all the nutrients have chemical energy (because they are molecules and have chemical bonds), the living beings get most of the energy they need from just carbohydrates and lipids, so you are more likely to obtain energy from pasta (rich in carbohydrates) than from chicken meat (rich in proteins).|
|Fossil fuels||Coal, oil (or petroleum) and natural gas. They are called fossil fuels because they come from the buried and highly transformed remains of organisms that lived in the past (plankton for natural gas and oil, woody ferns for coal). They are mixtures of molecules called hydrocarbons (such as the octane of the petrol or gasoline), and they are widely used as fuels because the chemical energy of the hydrocarbons is transformed into large amounts of heat when the hydrocarbons are ignited.|
|Nuclear||It takes advantage of the large amounts of heat released when the nucleus of an atom is broken. This is achieved by making lonely neutrons strike the nuclei of atoms of uranium or plutonium, thus making two or three neutrons beeing expelled away from bombarded nuclei, along with a lot of heat, that can later be used in a nuclear power plant to produce electricity.|
|Biomass||Burning certain structures of living beings that are rich in chemical energy (such as the wood or the peat) also releases great amounts of heat that can be harnessed by humans with several purposes, that range from heating a house to producing electricity in a biomass power plant.|
|Aeolic||The kinetic energy of the moving air can be used by humans: in a windmill to grind flour, in an aerogenerator to produce electricity, etc…|
|Hydraulic||The kinetic energy of a water current (such as a river) can also be used for similar purposes, for instance in a watermill or in a hydroelectric power station.|
|Solar||The energy contained in the light radiations can be used, for instance, to heat water for domestic supply, or to produce electricity in a solar field.|
The goal of power plants is to produce electricity that is later dumped into the general supply network. That electricity is produced by an electrical generator driven by a turbine, in all cases. The differences between the several types of power plants come with the way in which that turbine is moved:
- In the hydroelectric power stations, it is the water flow of a river what moves the turbine.
- In an aerogenerator it is the wind what moves the turbine (which consists of a set of three big blades).
- In the rest of the cases it is water vapour at a very high pressure what moves the turbine. That water vapour is produced by heating water, and the heat can come from…
- igniting coal or other fossil fuels or biomass (in thermal power plants);
- breaking nuclei of uranium or plutonium (in nuclear power plants).
This way, the production of heat in a power plant goes through a series of stages in which a transfer and a transformation of energy take place. The following diagram summarizes what happens in a coal-fueled thermal power plant:
- Chemical energy in the coal -> Thermal energy in the water vapour -> Kinetic energy in the turbine -> Electric energy in the generator and to the supply network wires