Potential energy is energy that is stored, but how it is stored depends on its type, such as chemical, physical or electrical energy. Potential energy stays in storage until the situation changes and the potential energy is released. The release can be controlled and can perform useful work, or it can be sudden and harmful. Whenever potential energy is present in large quantities, an awareness of the amount of potential energy and what might trigger its release is important for safety and for avoiding an uncontrolled, destructive release.
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Potential energy is stored chemical, physical, electrical or other energy that can be released when triggered. Chemical energy is stored in chemical bonds and is released during chemical reactions. Physical energy is stored when a mass is held above its zero-height resting place or when a structure is stressed or deformed. Electrical energy is stored in electric or magnetic fields and in accumulations of charged particles. Other types of potential energy include atomic energy and thermal energy. For each type of potential energy, there are applications for useful work and triggers for destructive release.
Chemical Potential Energy
In chemistry, potential energy is stored in chemical bonds. Chemical reactions can liberate chemical potential energy and create new compounds or produce heat and light. Chemical reactions are used to power machines such as car motors or to heat buildings by burning fuels. Explosives also release chemical energy and can be constructive or destructive.
Physical Potential Energy
Potential energy in physics is stored either in gravitational energy or as elastic energy. Gravitational energy is due to the elevated position of a body that has mass. The greater the mass, the more potential energy is stored. When the mass is released and drops, the potential energy changes to kinetic energy as the mass picks up speed. The resulting kinetic energy can be useful, such as when it drives piles into the ground, or dangerous, such as when a bridge collapses.
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Elastic energy is stored in the deformation of a structure. For example, a spring has a normal shape, but when compressed or stretched, it stores potential energy. When released, the potential energy can do work or it can cause damage. The spring in a non-electric wrist watch is deformed by winding up the watch, and the potential energy powers the watch. An elastic band stores potential energy when stretched, but if it breaks or is let go, the potential energy can hurt.
Electrical Potential Energy
While batteries produce electricity, the process at the root of battery power is a chemical reaction. The reaction creates an imbalance of electrons that produces an electric charge across the battery terminals. As a result, batteries store both chemical and electrical energy.
Pure electric energy is stored in the electric fields of capacitors. Small capacitors help electronic circuits function and larger ones are found in fluorescent lights and some electric motors. If a large capacitor short circuits, the potential energy is released all at once and can cause an explosion or fire.
Other Types of Potential Energy
Other forms of potential energy include atomic and thermal energy. Uranium atoms store nuclear energy that can be released in atomic fission reactions. Hydrogen atoms store nuclear energy that powers fusion reactions such as in the sun and in hydrogen bombs. Other elements may store nuclear potential energy that can be released in reactions not yet discovered or that are known but are not used. The fission reactions power nuclear reactors but they can also be used in atomic bombs.
Thermal energy is the energy of a substance such as a gas in a container. The internal energy of the gas is actually kinetic energy at a molecular level because the gas pressure is caused by the action of the gas molecules bouncing against the container walls. It is potential energy because the gas in the container has stored energy that can do work when the gas flows into another container with less pressure. If the gas pressure is too high the container may burst, releasing all the potential energy at once in an explosion.
Potential energy is useful because it can be kept in storage until it is needed or moved to where it is needed. In each case, there is a danger of triggering an accidental release of the potential energy. As a result, potential energy has to be handled carefully to ensure it fulfills its intended function and doesn't cause any damage.