Feature Report: What Is Energy?

3 items of content in this feature report



Energy’s Main Properties

The energy contained in matter is invisible, but light, movement, wind, and waves are some of the ways it manifests itself. Whether in its natural form or harnessed by humans, energy can be transmitted from one object to another, often through conversion. However, it cannot be created or destroyed: the universe contains a constant, finite amount of energy.  

fr - energie caracteristiques
Electric currents are found in nature. The best-known examples include lightning and electric fish. © THINKSTOCK

Primary Energy Versus Secondary Energy

Primary energyAll energy sources that have not undergone any conversion process and remain in their natural state.. is a form of energy found in nature. Examples include energy from muscles (humans and animals), water (river currents, tides and waves), wind and fuelFuel is any solid, liquid or gaseous substance or material that can be combined with an oxidant... (oil, coalCoal is ranked by its degree of transformation or maturity, increasing in carbon content from... , biomassIn the energy sector, biomass is defined as all organic matter of plant or animal origin... ). But static electricityStatic electricity is the accumulation of an electric charge in an insulating material... produced by friction between some materials and the energy from lightning are not considered to be primary energy, because they cannot be harnessed.

Primary energy used on an industrial scale can be broken down into renewable energies (sunlight, water, wind, biomass, etc.) and non-renewable energies such as fossil fuels (oil, coal and gas). Nuclear energyEnergy produced in nuclear power plants. The enormous amount of heat released during fission of uranium atom nuclei is transferred to water... (produced by the fission of uraniumGray, very dense radioactive metal that is relatively abundant in the Earth's crust and oceans in the form of UO2... and plutonium nuclei) is also a form of primary energy.



For the most part, secondary energySecondary energy is energy produced by converting so-called primary energy, or energy available in its natural state in the environment... , also called energy carriers, is usually converted by humans from primary energy sources. For example, electricityForm of energy resulting from the movement of charged particles (electrons) through a conductor... generated from gas, coal, water, wind or sunlight is a secondary energy. Fuel is another example.

Secondary energy is then converted into final energy available to the user, such as light (in light bulbs), heatIn the field of statistical thermodynamics today, heat refers to the transfer of the thermal agitation of the particles making up matter... (radiators) and mechanical energySum of the potential energy and kinetic energy of an object or system... (fans, engines, pumps, etc.).



Different Amounts of Energy in Different Objects

All matter and objects contain a certain amount of energy, which varies according to their properties (position, mass, shape, speed, etc.) For example, a compressed spring contains far more energy than a spring that is not compressed. A raised object has more potential energyEnergy contained in an object or physical system that has the potential to be converted into kinetic energy... than an object on the ground. And the faster an object is moving, the more kinetic energyThe energy of an object due to its motion. it has.

Energy Transmission and Conversion

Energy can be transmitted from one object or system (a set of connected things or parts) to another. The heat from a radiator is transferred to the air of the room it is in. On a bicycle, the movement of the pedals is transmitted to the wheels. When one marble hits another, it transmits a certain amount of motion.

However, energy often changes form when transmitted. For example, the energy contained in wood is converted into heat and light when it is burned. Wind energyEnergy derived from the wind. Wind power involves converting the kinetic energy of moving air (wind) into electricity. captured by a wind turbine is converted into mechanical energy, which itself is converted into electricity by a generator. Energy from the Sun is converted into growth factors by plants thanks to a process called photosynthesisProcess used by plants to fuel their growth. Light energy from the Sun is utilized to convert carbon dioxide and water into carbohydrates...

The amount of energy contained in the universe is finite and constant.  

The law of conservation of mass (or matter) discovered by 18th-century chemist Antoine de Lavoisier states that “nothing is lost, nothing is created, everything is transformed." This applies to energy too. Energy cannot be created or destroyed, only be transmitted or converted. The total amount of energy remains constant, even when it seems to have disappeared.

For example, if you roll a marble on the ground, it slows down and stops, having gradually run out of kinetic energy due to friction. But this does not mean that there is no energy left: the energy has been converted into heat and transmitted to the ground and the air. In fact, the total amount of energy contained in the universe is finite and constant.

When we speak about generating energy, we are not really creating it, but converting it.