Energy is defined by scientists as the ability to perform work. People have learned how to convert energy from one form to another and then use it to do work, which makes modern civilization possible. People use energy to walk and bike, drive cars on roads, cook food on stoves, make ice in freezers, light our homes and offices, manufacture products and send astronauts into space. Heat, light, motion, electrical, chemical and gravitational energy are all examples of different types of energy. These types of energy can be divided into two categories: potential or stored energy and kinetic or working energy.
Energy can be transformed from one state to another. For example, food contains chemical energy, which a person’s body stores until he or she uses it as kinetic energy during work or play. The chemical energy stored in coal or natural gas, as well as the kinetic energy of flowing water in rivers, can be converted to electrical energy, which can then be converted to light and heat.
What is energy?
Energy is defined as the ability of a body to do work. It can also be defined as the force that causes things to move. Energy is shifted from one place to another by doing work. Energy is a scalar quantity. According to law of conservation of energy, Energy cannot be created or destroyed, however its form changes. It remains conserved (the total amount of energy does not change) in all phenomena.
How energy is transferred?
When the energy travels from one point to another, then it is known as energy transfer. There are 4 basic ways, by which energy gets transferred.
- By mechanical way
- By electrical way
- By radiations (light and sound waves)
- By heating (conduction, convection and radiation)
For example, sound energy gets transferred by the vibration of particles, similarly in case of water waves. However, thermal energy is transferred by conduction, convection or radiation. For example, in case of light, energy is transferred by radiations.
Units of energy
There are many units of energy, according to different cases, which are categorized into basic and source based units. The common units of energy are joule, kilo watt hour, electron volt etc, all of which fall in basic units, as source based units are linked to the specific properties of fuel.
Joule (J): This is the basic SI unit of energy. It is ultimately defined in terms of the meter, kilogram and second. Since
W = F . d
So, 1 J = (kg. m2)/ s2
Calorie (cal): Calorie is defined in terms of the heating of water. Thus, in a traditional definition, one calorie is the amount of heat that is required to raise the temperature of 1 gram of water by 1°C.
1 cal = 4. 184 J
British thermal unit (Btu): This is the English system analog of the calorie.
1 Btu = 251.99 cal.
Kilowatt-hour (kWh): The kilowatt-hour is a standard unit of electricity production and consumption. By definition, 1 kilowatt = 1000 watts:
1 kWh = 3.6 x 106 J
Electron volt (eV): This unit of energy is used for micro level or atomic level. As joule is a bigger unit than electron volt, so that is just used for macro-level.
1 eV = 1.6 x 10-19 J
Other units of energy and their relation is given as:
Main types of energy
Usually, energy is classified into kinetic and potential, and all other types of energy are taken as sub types of kinetic or potential. Here we will discuss all types of energy in detail.
What is kinetic energy?
The energy which is required in any kind of motion is known as kinetic energy. It is measured as
K.E = (1 / 2) m v2
Where m is the mass of object and v is the velocity, with which object is moving.
Types of kinetic energy
What is radiant energy?
Radiant energy is a type of electromagnetic energy which is experienced in form of heat. It travels in the form of waves or particles. It can be visible (light) or invisible (radio or x-rays). Sunlight is an example of radian energy.
This term is mostly used in solar energy, heating, radiometry and lighting. As electromagnetic radiations travel as a stream of photons, so in case of radiant energy, it can be considered that the energy is carried by these photons. Like all EM radiation, energy is carried in oscillating electric and magnetic fields of these waves.
What is thermal energy?
Thermal energy which is also termed as heat energy, is produced with the rise of temperature. This rise causes atoms and molecules to move/vibrate faster and collide with each other with enhanced energy.
Thermal energy is also related to the internal energy of system. When external temperature is increased, then their internal energy increases due to the increase in thermal energy (since internal energy is sum of all energies). Due to which molecules vibrate faster.
What is sound energy?
Is sound a form of energy? The answer is yes. However, unlike light energy, sound energy needs a medium to pass, so sound cannot pass through vacuum. Sound energy travels in the form of waves. Sound energy gets transmitted by solids, liquids and gases. It travels faster through solids as compared to gases, as the atoms in solids are closer to each other.
It is an energy form which humans can hear, but only those sounds are audible to humans which lie in the frequency range of 16 Hz to 20 KHz. When sound is produced through some source, then it produces vibrations in air, just in front of that source, then with the help of air molecules motion, this sound wave gets shifted to another location. This is the way, how sound travels.
What is electrical energy?
This type of energy is caused due to the motion of electric charges like electrons. The electrons will carry more electrical energy, if they move faster. Batteries and cells are the sources of electrical energy.
Electrical energy is considered as a type of potential energy because this energy is stored due to relative positions of charged particles (as charges are static). This energy will no longer remain as electric, if charges start motion, then it will become as magnetic.
What is mechanical energy?
It is the energy, which is stored in objects as they move. It is the sum of kinetic and potential energy. More energy will be stored, if objects move faster. For example, when a pendulum is at mean position it only has potential energy.
Now if we displace it to the extreme position, then potential energy will increase.
As we leave pendulum, its potential energy starts decreasing and kinetic energy increases.
Then it continues its to and fro motion. Its energy keeps changing from one form to another but the total mechanical energy is same.
Its other examples include, spring compressing and stretching, hitting a nail with hammer, motion of swing etc.
What is light energy?
Is light a form of energy? Yes light is also an energy type. Light energy is a form of electromagnetic radiation. It consists of photons and travels in form of waves. This is the only type of energy, which is visible to human eye.
It falls in category of kinetic energy, as light is never at rest. Its sources can be lasers, sun, bulbs etc. when an atom is provided by energy, then its electrons move from lower energy level to higher energy level. Since these electrons are not stable in higher level, so they return back, which results the emission of photons. Light has the highest speed n universe, as light photons carry no mass. Speed of light is 3 x 108 m / s.
What is potential energy?
The energy that an object possesses due to its position is known as potential energy. It is measured as
U = m g h
Where m is mass of object, g is gravitational acceleration and h is the height of object.
Types of potential energy
What is Gravitational potential energy?
This energy is associated with gravity. An object at certain height will have more gravitational potential energy as compared to an object, which is at ground level.
Gravitational potential energy means the work done to bring a unit mass from one point to another, against the action of gravity. It is given as
U = – G M m / r
Due to inverse law, the gravitational potential energy becomes zero when r becomes infinity. This negative sign indicates the bound state of objects with each other.
What is nuclear energy?
As clear from the name, this energy comes from the nucleus of the atom. This energy gets released during the nuclear fission reaction, when the nuclei split apart.
In a nuclear reactor, when a heavy nucleus breaks, then a huge amount of nuclear energy is produced. The heat that is released by this fission reaction is then used to create steam which spins a turbine to generate electricity.
Define elastic energy
When an external force produces some deformation in an object, then the energy is stored in that object, which is known as elastic energy. This energy is stored in the bonds, which hold the atoms together. As the external stress is removed, the bonds release that absorbed energy. This factor makes a variety of things elastic.
Definitely, bonds can absorb energy, up to some limited extent. When more stress is applied, then these bonds don’t come back to original shape or even break, when stress is removed. This factor makes them as plastic materials. Elastic potential energy is given by
U = (1 / 2) k x2
Elasticity can also be termed as the reversibility of a material. However, all materials have some degree of distortion which they can endure without breaking.
Define chemical energy
Chemical energy releases when the chemical reaction takes place. It is stored in the bonds of chemical compounds. Usually, after the release of chemical energy, substance completely transforms into a new substance. Chemical energy may get released during the chemical reaction in the form of heat, such reactions are known as exothermic reactions.
The food that we eat provides us chemical energy, which is then converted to mechanical energy and heat. The chemical energy of a battery or cell is converted into electrical energy.