Simply put, energy is the ability to do work, which is a physics term to describe moving objects with some force across some distance. There are several different forms of energy, and it can be transformed from one form to another. Potential, kinetic, and thermal energy share many attributes and elements, but they describe distinct (albeit closely related) processes.
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The Law of Conservation of Energy from Thermodynamics importantly describes that energy can change from one form to another, but it can never be created or destroyed. This means the total energy in a closed system (like the universe) is constant.
Potential energy is the stored energy, waiting to be released. This can be found across almost all systems: chemical bonds, nuclear energy, electrical potential energy, and mechanical energy (like gravitational potential energy and elastic potential).
An illustration of a form of potential energy might be stretching a rubber band. Stretching the elastic band builds up energy, preparing the energy to be released through mechanical motion. This is referred to as elastic potential energy.
Gravitational energy is another type of potential energy that results from a gravitational force exerted on objects. Potential energy is stored within a mass or object elevated above a gravitational body (like the Earth) until it begins to move from the force of gravity.
Chemical potential energy stored in the bonds between molecules and atoms stores energy found in food, materials, and fuel; it is a crucial piece of a chemical reaction. Electric charge and the movement of electrons to create current and electrical power is also heavily reliant on electric potential energy, also called voltage.
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We are still learning about how gravitational fields and forces operate, but the gravity of a body in space can be understood as the mass of the object interacting with spacetime.
Kinetic energy is the energy of motion. Potential energy is converted to kinetic energy when the object in question begins to move.
There are three types of kinetic energy: vibrational, rotational and translational. Each type of kinetic energy is named according to the type of movement the object experiences or performs. Vibrational kinetic energy is expressed as an object’s vibrational motion (e.g. sound energy); rotational kinetic energy occurs when an object rotates or turns (e.g. a pulley wheel); translational kinetic energy refers to an object moving from one location to another (e.g. running around a track).
Various forms of kinetic energy come from different sources and forces. Some kinetic energy might be expressed as potential internal energy is expressed as outward motion. Other kinetic energy might result from external forces like gravity. The kinetic energy of an object can be easy to observe because of its visible expression, but some forms of kinetic energy might be felt in surprising ways.
The physics of heat energy also describes thermal energy. Atoms and molecules of an object vibrate and bump together, producing heat, and as vibration increases, thermal energy is expressed. This vibration might sound familiar, as thermal energy can actually be considered a special expression of kinetic energy.
Although heat and thermal energy are related, there is a difference between the two. Heat describes the transfer of thermal energy in a system, while thermal energy actually measures the state of this heat energy in a system. Thermal energy also deals with properties of heat transfer like conduction and radiation.
There are many sources of energy production that hinge upon thermal energy like coal and nuclear power plants.
Kinetic and potential energy are measured in joules. One joule is equivalent to the amount of energy used when one newton of force is used to move an object one meter of distance. Thermal energy is measured in therms. One therm is equal to 100,000 British thermal units, or 1,055 joules. One British thermal unit refers to the amount of energy needed to raise the temperature of water one degree Fahrenheit.
- The Physics Classroom: Work, Energy, and Power - Lesson 1: Potential Energy
- The Physics Classroom: Work, Energy, and Power - Lesson 1; Kinetic Energy
- InnovateUs Inc.: What is Thermal Energy?
- California Energy Commission: Chapter 1; Energy - What Is It?
- University of Wisconsin-Stevens Point: Energy Rules!
- University of Wisconsin-Stevens Point: What is Energy?
About the Author
Amanda Davis began writing in 2010 with work published on various websites. Davis is a dietetic technician, registered, personal trainer and fitness instructor. She has experience working with a variety of ages, fitness levels and medical conditions. She holds a dual Bachelor of Science in exercise science and nutrition from Appalachian State University and is working toward her master's degree in public health. Davis will be a registry eligible dietitian in May 2015.