1.1: Forms of energy
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Six Basic Forms of Energy
There are 6 basic forms of energy:
- Mechanical energy
- Chemical energy
- Thermal or heat energy
- Electrical energy
- Nuclear energy
- Radiation
1. Mechanical Energy
There are two types of mechanical energy: kinetic and potential energy.
Kinetic energy is the energy that a body possesses due to its motion. Bodies that contain kinetic energy include a baseball traveling through the air after being thrown or a hammer pounding nails. In the United States, about 1/3 of the total energy produced is used for transportation or movement of people and goods.
Potential energy is the energy that a body possesses due to its position relative to a reference point. Bodies that contain potential energy include a pendulum at the top of its oscillation or a compressed spring.
Additional Information
A book sitting on a shelf in the library is said to have potential energy because if it is nudged off the shelf, gravity will accelerate the book, giving the book kinetic energy. Because the Earth's gravity is necessary to create this kinetic energy, and because this gravity depends on the Earth being present, we say that the Earth-book system is what really possesses this potential energy, and that this energy is converted into kinetic energy as the book falls.
2. Chemical Energy
Chemical energy is the potential energy contained in molecular bonds, which exists due to electric and magnetic forces of attraction that different parts of molecules exert. It is also referred to as "microscopic potential energy". This attractive force is the same force involved in thermal vibrations. When chemical reactions occur and the molecule is rearranged, the chemical energy can increase or decrease. Examples of bodies with chemical energy include batteries and glucose in the human body.
About 85% of the energy used in the U.S. is from fossil fuels like natural gas, coal, and oil, which all store chemical energy. Burning these fossil fuels releases thermal or heat energy which is then used to power various processes.
Additional Information
The glucose (blood sugar) in your body is said to have "chemical energy" because the glucose releases energy when chemically reacted (combusted) with oxygen. Your muscles use this energy to generate mechanical force (work) and also heat.
3. Thermal or Heat Energy
Thermal energy is a combination of the microscopic, kinetic, and potential energy of molecules. Examples of bodies with thermal energy include boiling water and a hot beverage.
Temperature is a measure of how much thermal energy a body has. At higher temperatures, molecules are moving faster and/or vibrating, thus having more kinetic and potential energy. Movements contribute kinetic energy while vibrations contribute potential energy for molecules.
Additional Information
A hot cup of coffee is said to possess "thermal energy," or "heat energy," because it has a combination of kinetic energy (its molecules are moving and vibrating) and potential energy (the molecules have a mutual attraction for one another) - much the same way that the book on the bookshelf and the Earth have potential energy because they attract each other.
4. Electrical Energy
Electrical energy is created from the movements of electrons in matter. It is commonly converted into other forms of energy. For example, toasters convert electricity to thermal energy, and speakers convert electricity to sound. Because of the numerous applications, electricity is in high demand. In the U.S. alone, about 40% of the total primary energy used is converted into electricity.
Important Point
All matter is made up of atoms, and atoms are made up of smaller particles called protons (which have positive charge), neutrons (which have neutral charge), and electrons (which are negatively charged).
- The electrons orbit around the nucleus (which contains protons and neutrons), just like the planets orbit the sun.
- Certain metals have electrons that are only loosely attached to their atoms, so they can be easily made to move from one atom to another if an electric field is applied to them.
- When those electrons move among the atoms of matter, a current of electricity is created.
5. Nuclear Energy
Nuclear energy is produced when reactions in an atom cause a structural change in the nucleus. There are two main types of nuclear reactions: fusion and fission.
Fusion is when two nuclei join together to form one larger nucleus or particle. This releases energy in the form of light and heat. Fusion occurs in the Sun, where hydrogen nuclei fuse together to make helium nuclei, releasing energy.
Fission is when the nucleus of one atom splits into two smaller atoms. Like fusion, this also releases energy as light and heat. Nuclear reactors and the Earth's interior depend on fission, usually involving uranium as the atom being split.
Additional Information
In both fusion and fission, some of the matter making up the nuclei is converted into energy, represented by the famous equation
\[ E = mc^2 \nonumber\]
where \( E \) is energy, \( m \) is mass, and \( c \) is the speed of light.
- This formula indicates that energy intrinsically stored in matter at rest equals its mass times the speed of light squared. When matter is destroyed, the energy stored is released.
- This equation suggests that an incredibly huge amount of energy is released when a small amount of matter is converted to energy.
6. Radiation
Radiation is energy transmitted in the form of rays, waves, or particles. Examples of radiation include ultraviolet (UV) and microwave radiation. Electromagnetic radiation is a type of energy that oscillates and is comprised of electric and magnetic fields that travel freely through space. Electromagnetic radiation is comprised of photons, which can be thought of as discrete "packets" of energy with properties of waves. Photons are created when electrons transition from higher to lower energy levels in atoms and absorbed when electrons transition from lower to higher energy levels. Photons are also created when a charged particle, like an electron, is accelerated. This occurs in radio transmitter antennae, which generate radio waves.
The electromagnetic spectrum represents the various types of electromagnetic radiation that occur at different wavelengths and frequencies, which are inversely related.
The following video explains the electromagnetic spectrum.
As shown in the video, the lower the energy, the longer the wavelength and lower the frequency, and vice versa.
Staring directly at the Sun hurts our eyes because it contains UV light, which contains high-energy (i.e., high frequency and low wavelength) photons, and this energy can cause physical damage to cells. Humans can only see visible light, because other forms of electromagnetic radiation outside of the visible light spectrum have wavelengths/frequencies that are outside of what the human eye can perceive. A great discovery of the 19th century was that radio waves, X-rays, and gamma rays (types of electromagnetic radiation) are just forms of light, and that light is just electromagnetic waves.
About 20% of electricity used in the U.S. is used to produce visible light.