Energy is the capacity of a physical system to do work.
- It is quantified through metrics.
Energy is derived from the utilization of physical or chemical resources.
- one Newton force is the force required to accelerate an object with a mass of 1 Kilogram over a 1 meter distance, over a period of 1 second per second.
Matter is equivalent to energy in the sense that the two are related by the equation E=mc2
Energy can be stored in different ways, including:
- Chemical. The energy stored in chemical bonds, such as those between molecules.
- Elastic potential. The energy stored when an object is stretched or squashed.
- Electrostatic. The energy stored when repelling charges have been moved closer together or when attracting charges have been pulled further apart.
- Gravitational potential. The energy of an object at height.
- Kinetic. The energy of a moving object.
- Magnetic. The energy stored when repelling poles have been pushed closer together or when attracting poles have been pulled further apart.
- Thermal (Internal). The total kinetic and potential energy of the particles in an object, in most cases the vibrations - also known as the kinetic energy - of particles. In hotter objects, the particles have more internal energy and vibrate faster.
Energy can remain in the same store for millions of years or for just a fraction of a second. Energy transfers occur all the time - whenever a system changes there is a change in the way some or all of the energy is stored. Examples of energy transfers include:
- electrical work - charges moving due to a potential difference
- heating - due to temperature difference caused electrically or by chemical reaction
- mechanical work - a force moving an object over a distance
- radiation - energy transferred as a wave, such as light and infrared emitted from a star.
Whenever there is a change in a system, energy is transferred and some of that energy is dissipated.
Dissipation is a term that is used to describe ways in which energy is wasted. Any energy that is not transferred to useful energy stores is said to be wasted because it is lost to the surroundings. The ways in which energy is dissipated depends on the system.
- For a device such as a radio communicator, the electrical work is transferred into useful sound and infrared radiation is dissipated – that is, wasted as thermal energy (heat).
- For a device such as a vehicle motor, the mechanical work is transferred into physical motion and both kinetic energy and infrared radiation is dissipated – that is, wasted as vibration and thermal energy (heat).
Energy can be stored, transferred usefully, or dissipated, but it cannot be created or destroyed, only changed from one form to another. This principle is known as the conservation of energy, or the first law of thermodynamics. All the energy in the universe was present at the Big Bang and will still be around at the very end of time.
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