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Energy

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Quick
There are many different types of energy such as heat and work. Often people will start with one type of energy and then change it into other, more usable, types.The SI unit of energy is the joule [J], which is a Newton-meter [Nm]


Different Types of Engineering Energy

Type	Quick Description	Formula(s)
Work	Force times distance	W = Fxd
Heat	Due to a temperature difference between two bodies
Mechanical Energy	Sum of kinetic and potential energy	Emech = K + U
Gravitational Potential Energy	Energy due to gravity	U(z) = mgy
Elastic Potential Energy	Springs	U(x) = 1 2 kx2
Kinetic Energy	Energy of motion, objects in motion	EK = 1 2 mu2
Potential Energy	Stored energy	ΔU = –W
Thermal Energy	Commonly called heat	ΔEth = fkd    due to sliding (friction)
Internal Energy	Other unaccounted forms of energy aside from mechanical energy
Intermolecular potential energy	Involves the forces between molecules
Molecular kinetic energy	Involves the translational velocity of individual molecules
Intramolecular energy	(Energy within the individual molecules) involves the molecular and atomic structure and related forces
Strain energy	The increase in energy associated with the deformation of a member.

Other Types of Energy

Sound	Sound energy is the movement molecules in the air that produces vibrations. Alarms, music, speech, ultrasound medical equipment all use sound energy. VCR tapes change sound energy into electrical energy. The electrical energy records the sound using magnetic tape. Speakers read the magnetic tape and change it back into sound.
Hydroelectric
Nuclear	Nuclear energy is the energy stored within atoms. Nuclear energy is unusual in that it can give off energy in the form of light or heat, but it is the change in the atom's makeup that produces the energy. Submarines, power plants, and smoke detectors all use nuclear energy. Nuclear power plants use uranium, a radioactive element, to create electricity.
Chemical (example: Fire)	Chemical energy is stored in the bonds of molecules. This is a form of potential energy until the bonds are broken. Fossil fuels and biomass store chemical energy. Products that contain chemical energy include: TNT, baking soda, and a match.
Solar (example: Light)
Other waves (example: radio, micro, gamma, etc.)
Wind
Gravitational	Gravitational energy is the attraction between two objects. The moon in its orbit around the earth, the earth in its orbit around the sun, the ocean's tides, your ability to stay on the ground instead of floating into the atmosphere are all examples of gravitational energy. Research is going on in this field. Waves may be harnessed in the future to provide electrical energy.
Electromagnetic
Magnetic	Magnetic energy is the attraction of objects made of iron. Medical equipment (MRI scanning), compass, refrigerator magnets are all examples of magnetic energy. Any type of energy source that uses a generator in the process to make electricity uses magnetic energy.
Electrical / Electronic	The movement of electrically charged particles produces electrical energy. Lightning, and static electricity are examples of electrical energy that occur naturally. (Static electricity is what you see when your clothes stick together.) Science hasn't found a way to use natural forms of electrical energy, like lightning. Instead, we use different energy sources to create electrical energy by using generators and turbines.
Sound Energy
Light Energy	Light energy is the movement of photons. (The light spectrum of electromagnetic waves shows light energy.) All life on earth is dependent on light energy from the sun. Examples of light energy include radio waves (AM, FM, TV), microwaves, X-rays, and plant growth. Active solar energy uses photovoltaic panels and light to turn light energy into chemical energy.
Radioactive energy (example: radioactivity)
Geothermal energy
Strain energy
Elastic energy
Translational (kinetic) energy
Rotational energy
Vibrational energy
Surface energy
Plasma

Details

Energy is defined as the ability to do work. Work is done when a force applied to some object moves the object. For example, lifting a heavy box is work. There are a number of types of energy: thermal energy, which is commonly called heat, electrical energy, radiant energy (including light), chemical energy, mechanical energy (including sound), and nuclear energy.

Energy can also be classified as kinetic energy or potential energy. Kinetic energy is energy of motion. Potential energy is stored energy. For example, a book on your desk has greater potential energy than the same book on the floor. When the book is dropped, it loses potential energy and gains kinetic energy as it falls.

Energy can be transferred from one object to another. For example, thermal energy can be transferred from a burner on the stove to a kettle of water. One form of energy can be changed into another form. For example, when magnesium and oxygen from air react to form magnesium oxide, chemical energy stored in magnesium and oxygen is changed into thermal energy and light energy.

The purpose of carrying out many chemical reactioins is to change chemical energy into other forms of energy. For example, the motor in a car changes energy from burning gasoline into mechanical energy; the battery in a flashlight changes chemical energy into electrical energy.

Energy is very important in the study of thermodynamics. Energy is a fundamental concept, such as mass or force and, as is often the case with such concepts, is very difficult to define. Energy has been defined as the capability to produce an effect. Fortunately the word energy and the basic concept that this word represents are familiar in everyday usage.

Energy can be stored within a system and can be transferred (as heat, for example) from one system to another. In a study of statistical thermodynamics one would examine, from a molecular view, the ways in which energy can be stored.

Consider a diatomic molecule, such as oxygen, as shown. In addition to translation of the molecule as a solid body, the molecule can rotate about its center of mass in two normal directions, about the x-axis and about the z-axis (rotation about the y-axis is negligible), and the two atoms can also vibrate, that is, stretch the bond joining the atoms along the y-axis. A more rapid rotation increases the rotational energy, and a stronger vibration results in an increase of vibrational energy of the molecule.

More complex molecules, such as typical polyatomic molecules, are usually three-dimensional in structure and have multiple vibrational modes, each of which contributes to the energy storage of the molecule. The more complicated the molecule is, the larger the number of degrees of freedom that exist for energy storage.

Let heat be transferred to water. During this process the temperature of the liquid and vapor (steam) will increase, and eventually all the liquid will become vapor. From the macroscopic view concern lies only with the energy that is transferred as heat, the change in properties, such as temperature and pressure, and the total amount of energy (relative to some base) that the H₂O contains at any instant. Thus, questions about how energy is stored in the H₂O are not of concern. From a microscopic viewpoint interest lies within the way in which energy is stored in the molecules. There might be interest in developing a model of the molecule so that the amount of energy required to change the temperature a given amount can be predicted.

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