Energies

Energy is conserved, converted, exploited

From Thermodynamics to Quantum

The word energy derives from the Ancient Greek, energeia, or 'activity'. Gottfried Leibniz proposed the idea of the Latin: vis viva, or living force, which defined as the product of the mass of an object and its velocity squared; he believed that total vis viva was conserved. To account for slowing due to friction, Leibniz theorized that thermal energy consisted of the motions of the constituent parts of matter, although it would be more than a century until this was generally accepted. The modern analog of this property, kinetic energy, differs from vis viva only by a factor of two. Emilie du Châtelet proposed the concept of conservation of energy in the marginalia of her French language translation of Newton's Principia Mathematica.

In 1807, Thomas Young was the first to use the term "energy" instead of vis viva, in its modern sense. Gustave-Gaspard Coriolis described "kinetic energy" in 1829 in its modern sense, and in 1853, William Rankine coined the term "potential energy". It was argued for some years whether heat was a physical substance, or merely a physical quantity until 1845 when James Prescott Joule discovered the link between mechanical work and the generation of heat.

These developments led to the theory of conservation of energy, formalized largely by William Thomson (Lord Kelvin) as the field of thermodynamics. Thermodynamics aided the rapid development of explanations of chemical processes by Rudolf Clausius, Josiah Willard Gibbs, Walther Nernst, and others. It also led to a mathematical formulation of the concept of entropy by Clausius and to the introduction of laws of radiant energy by Jožef Stefan.

Albert Einstein's 1905 theory of special relativity showed that rest mass corresponds to an equivalent amount of rest energy. This means that rest mass can be converted to or from equivalent amounts of non-material forms of energy. According to Noether's theorem, the conservation of energy is a consequence of the fact that the laws of physics do not change over time. Thus, since 1918, theorists have understood that the law of conservation of energy is the direct mathematical consequence of the translational symmetry of the quantity conjugate to energy, namely time.

The first evidence of quantization in atoms was the observation of spectral lines in light from the sun in the early 1800s by Joseph von Fraunhofer and William Hyde Wollaston. The notion of quantized energy levels was proposed in 1913 by Niels Bohr. The modern quantum mechanical theory explaining these energy levels in terms of the Schrödinger equation was advanced by Erwin Schrödinger and Werner Heisenberg in 1926.

Conversion of Energy forms

Even though the definition of Energy is not obvious, there are many forms of ‘Energy’ that perturb the ‘void’ in the space-time with ‘waves’ according to the representations nowadays. The interconversion of Energy forms allowed Humans to settle and develop civilizations along history. The agricultural revolution was possible thanks to the control of Heat with the fire and the Mechanics provided by horses, mills, and wheels… With the scientific and industrial revolutions, the interconversion of Heat and Work became more efficient with Thermodynamics, and engines… Chemical reactions were used for this purpose, heating coal, and petroleum allowed the displacement of cars, trucks, ships, etc. The electrical form of Energy and the interconversion of electrical and chemical forms in batteries are another example...

Energy is neither created nor destroyed

The law of conservation of energy says that energy is neither created nor destroyed. When we use energy, it doesn't disappear, but instead, it changes from one form of energy into another form. A car engine burns gasoline, converting the chemical energy in gasoline into mechanical energy. Solar photovoltaic cells change radiant energy from the sun into electrical energy. Energy changes form, but the total amount of energy in the universe stays the same.

Energy is only converted

Energy efficiency is the amount of useful energy obtained from a system. A perfectly energy-efficient machine would convert all the energy it uses into useful work. Converting one form of energy into another form of energy always involves a conversion into useable and unusable energy. Reversibility is another feature of Energy conversion, it can be reversible or not, it depends on the amount dissipated during conversion. Gibbs equation shows how the free enthalpy is the only potion used or available in the total enthalpy, the rest is entropy.

Two main forms of Energy

Energy is grouped into two general categories i.e. ‘Potential’, or stored, ‘Kinetic’, or working. For example, the petroleum ‘a mixture of organic molecules’ contains a stored chemical energy, that is converted into kinetic energy during the displacement of a car equipped with an engine. The stored chemical energy in coal or natural gas and the kinetic energy of water flowing in rivers can be converted to electrical energy, which can be converted to light and heat.

Potential energy is stored

Chemical energy is energy stored in the bonds of atoms and molecules. Batteries, biomass, petroleum, natural gas, and coal are examples of chemical energy. For example, chemical energy is converted to thermal energy when people burn wood in a fireplace or burn gasoline in a car's engine.

Mechanical energy is energy stored in objects by tension. Compressed springs and stretched rubber bands are examples of stored mechanical energy.

Nuclear energy is energy stored in the nucleus of an atom, the energy that holds the nucleus together. Large amounts of energy can be released when the nuclei are combined or split apart.

Gravitational energy is energy stored in an object's height. The higher and heavier the object, the more gravitational energy is stored. When a person rides a bicycle down a steep hill and picks up speed, the gravitational energy is converting to motion energy. Hydropower is another example of gravitational energy, where gravity forces water down through a hydroelectric turbine to produce electricity.

Kinetic energy is motion

Radiant energy is electromagnetic energy that travels in transverse waves. Radiant energy includes visible light, x-rays, gamma rays, and radio waves. Light is one type of radiant energy. Sunshine is radiant energy, which provides the fuel and warmth that make life on earth possible.

Thermal energy, or heat, is the energy that comes from the movement of atoms and molecules in a substance. Heat increases when these particles move faster. Geothermal energy is the thermal energy in the earth.

Motion energy is energy stored in moving objects. The faster an object moves; the more energy is stored. It takes energy to get an object moving, and energy is released when an object slows down. Wind is an example of motion energy. A dramatic example of motion energy is a car crash, a car comes to a total stop and releases all of its motion energy at once in an uncontrolled instant.

Sound is energy moving through substances in longitudinal (compression or rarefaction) waves. Sound is produced when a force causes an object or substance to vibrate. The energy is transferred through the substance in a wave. Typically, the energy in sound is lower than in other forms of energy.

Electrical energy is delivered by tiny, charged particles, called electrons, that typically move through a wire. Lightning is an example of electrical energy in nature.

Renewability of Energy sources

The many different sources of energy are all either renewable or nonrenewable energy. Most energy sources used for doing work nowadays are nonrenewable e.g. Petroleum, Natural Gas, Coal, Nuclear Energy.

These energy sources are called nonrenewable because their supplies are limited to what we can mine or extract from the earth. Coal, natural gas, and petroleum took thousands of years to form from the buried remains of ancient sea plants and animals that lived millions of years ago, which is why we also call those energy sources fossil fuels. Nuclear energy is produced from uranium, a nonrenewable energy source whose atoms are split through a process called nuclear fission to create heat and, eventually, electricity.

The five major renewable energy sources include Solar energy from the sun, Geothermal energy from heat inside the earth, Wind energy from uneven heating from the sun, Biomass from plants, Hydropower from flowing water. Renewable energy sources are naturally replenished. Day after day, the sun shines, plants grow, wind blows, and rivers flow.

Throughout most of human history, biomass from plants was the main energy source. Biomass was burned to provide heat and light, to cook food, and to feed the animals people used for transportation and plowing. Nonrenewable energy began replacing most renewable energy in the early 1800s, and by the early-1900s, fossil fuel became the main source of energy. Biomass continued to be used for heating homes primarily in rural areas. In the mid-1980s, use of biomass and other forms of renewable energy began increasing largely to help reduce and avoid carbon dioxide emissions and climate change.