Energy is hard to define without resorting to mathematics, because energy is very abstract. This makes the simple question: "What is energy?" a tricky and subtle question to answer. One way to describe energy is that it can cause a push or pull over some distance. This leads to the idea that energy is the ability to create change. Objects and collections of objects have energy that can only be indirectly observed - by observing what energy does.

In order to be useful, energy has to be transformed or transferred. The transfer of energy involves concepts like work and heat, which also mean very specific things in the context of energy science. These definitions are slightly different from how the words are used in everyday language.

Energy is measured or denoted by many different units. These include units that are useful at the molecular level like electron volts (eV) to words used in the kitchen like calories. Physics classes tend to use units like joules, although chemists often favour calories. To make the units even more confusing the energy sector uses units like kilowatt-hours and BOE. There are also many large energy units useful for talking about energy use for whole countries like terawatt-hours and quads.

The rate that energy is used over time is known as power; visit energy vs power for a clear distinction.

Significance of energy

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Figure 1: Within this one image there are a number of different examples of energy in action: the boat's internal combustion engine, the well-lit buildings, and the lightning strike to name a few.[1]

Energy provides many useful energy services that allow for a high quality of life that people living in modernized societies have grown accustomed to.[2] These services require a constant supply of energy to power vehicles (internal combustion engines), feed populations, and generate electricity for billions of people, and it's the responsibility of energy industries to supply what's needed. This is done through an expansive collection of people, companies, and processes; all of which are necessary in the production, sale, and transportation of useful energy.

Energy also has the ability to cause damage or harm. For instance, burns are caused by an excess of thermal energy. Car accidents do a great deal of damage when the kinetic energy associated with driving down the street dissipates in a collision. Additionally, some processes used to harness energy can cause serious harm to the environment, and people specifically. Harnessing energy often leads to pollution and that leads to environmental consequences like climate change. Clearly, in order for society to properly utilize energy it should be properly understood and respected.

Types of energy

Energy cannot be created or destroyed: this is known as the law of conservation of energy, and it means that energy must be harvested from some source. No process can create energy, no matter how nice that would be. However, many processes can transform energy from one type (like those found in nature) into another (like those useful for energy services). There are many different forms or types of energy that can be sorted into three main categories:

Type of energy Examples Some ways of harnessing this energy
Kinetic energy Macroscopic kinetic energy
Microscopic kinetic energy
Wind power (macroscopic KE)
Tidal power (macroscopic KE)
Geothermal energy (microscopic KE)
Potential energy Gravitational
Fossil fuels
Nuclear power
Tidal power

Radiant energy Electromagnetic (light) Solar power

For more information on how energy can't be created or destroyed but can only be taken from available resources in nature, please visit the page: law of conservation of energy


For those who aren't familiar with the broad field of science, it should be noted that science uses very specific definitions for words, which are often different from everyday use. To a physicist, the word work means to exert a force over a distance - a process that (by definition) requires an input of energy. For example, a person does work on a refrigerator by pushing it a distance across the kitchen - she applies a force with her hands over the entire distance - to do so, energy must be expended by the person! This energy gets transferred into the sound of a refrigerator scraping along the floor, and even a slight increase in temperature of the bottom of the fridge and floor.

For more information visit the page: work


Heating can be both a desired and undesired result of energy utilization. For example, thermal energy heats houses and meals, which is obviously desirable - especially in colder climates. However, heat is also a byproduct of friction, which isn't always sought after. For instance, intricate parts in vehicles use lubricating oil to reduce friction, but if the oil runs out those intricate parts will be exposed to high levels of friction which typically leads to high heating and serious damage within the engine.

For more information visit the page: heat


Ultimately, most of the earth's energy comes from the nuclear fusion that takes place within the sun. This energy takes the form of light, which is otherwise known as electromagnetic radiation. In light, energy is transferred in little “packets” called photons that contain discrete amounts of energy that can propagate (as waves) over very long distances. When the photons hit an object, they transfer their energy to the object. It's important to note that all light, not just visible light, is like this. Light can have many different forms that are invisible to the unaided human eye. These different forms are classified by their wavelength and occupy a wide spectrum (known as the electromagnetic spectrum); differing ranges within this spectrum have differing levels of energy. From the highest energy to lowest are: gamma rays, x-rays, ultraviolet (UV), visible, infrared, microwave, and radio.

Figure 2. A visualization of the different wavelengths of light found within the electromagnetic spectrum, the right side of the spectrum contains wavelengths that are much higher in energy.[3]

For more information visit the page: light


  1. Quintano, Anthony. (2014, Aug. 20). Lightning over New York City July 2013 [Online]. Available:
  2. Scott, Smelling Land, 1st edition. Vancouver, Canada: Canadian Hydrogen Association, 2007
  3. (2014, Aug. 20). Manufacturing Electronic Microwave Components. [Online] Available:

Authors and Editors

Semaa Amin, Allison Campbell, Jordan Hanania, Braden Heffernan, James Jenden, Nathan Lefsrud, Ellen Lloyd, Amanda Musgrove, Jasdeep Toor, Jason Donev