# Energy

Energy can be defined as the capacity of a physical system to work. However, it is not necessary that the energy that exists is always available to do work. ## Types or forms of energy

The different types of energy can be grouped into two broad categories of energy that include kinetic energy (energy of a moving object) and potential energy (stored energy in an object). For example, energy can exist in different forms that include heat, chemical, nuclear, and electrical energy, etc., and each type either belongs to kinetic or potential energy. Here are energy types with their brief description.

### 1. Heat (Thermal) Energy:

It is also called thermal energy. It is related to temperature and it arises from the movement of atoms or molecules of a substance. When the temperature increases, atoms and molecules start moving fast and collide with each other to produce heat or thermal energy. The more the temperature rises, the hotter the substance and the greater its thermal energy will be. Here are some examples of thermal energy from our daily life:

• The warmth from the sun
• A cup of hot coffee
• Baking in an oven
• The heat from a heater

All the above objects have thermal energy due to their vibrating particles. For example, the hot chocolate has thermal energy owing to its vibrating particles and when we pour some cold milk into it some of its thermal energy is transferred to particles of milk so hot chocolate cools down as it has lost some of its thermal energy, whereas milk gets warmer as its particles start vibrating more after gaining heat from hot chocolate.

### 2. Electrical energy:

This type of energy is due to the movement of charged particles such as electrons, protons, ions, etc. It is directly proportional to the movement of charged particles, the faster the particles move, the more electrical energy they will have. As this energy arises owing to the movement of charged particles, so it is a type of kinetic energy. However, it is also considered potential energy as it also results from the relative positions of charged particles or electric fields. Some examples of electrical energy are as follows:

The car battery provides electrons that move in an electric current. These moving electrons provide electrical energy to the car.

When a thunderstorm occurs, the lightning that we see is electrical energy.

Electric eels are also capable of generating electrical energy which they use as protection from predators and to shock their prey.

### 3. Light Energy:

This form of energy is produced by electromagnetic radiation. Light comprises photons that are produced when the atoms of an object heat up. It is the only type of energy that can be seen with the human eye. Some common examples of light energy are stars, light bulbs, lasers, and hot objects.

It is the light energy that enables us to see such as naturally with the Sun or fire, or with artificial objects like candles, bulbs, etc. Light energy is also required by plants to produce their food.

### 4. Chemical Energy:

It is the energy stored in the chemical bonds that connect atoms of molecules and chemical compounds. It is produced or absorbed when chemical reactions occur. It is produced when the bonds between atoms or molecules break during a chemical reaction. Once a substance releases chemical energy, it is transformed into a new substance. As it is stored energy, it is a type of potential energy. For example, wood also has stored chemical energy, when the wood is burnt this chemical energy is released and converted into thermal energy and light energy and wood gets converted into ash, a new substance. Some examples of stored chemical energy:

• Biomass
• Coal
• Batteries
• Food
• Gasoline, etc.

All substances mentioned above have stored chemical energy. If we talk about food that we eat, it has stored chemical energy in the bonds between atoms in food. When these bonds break in a chemical reaction, energy is produced and new compounds are formed and new substances are formed. This energy is used by us to keep us warm, to move, and for growth and development.

### 5. Nuclear Energy:

This is the energy that comes from the nucleus of atoms due to the interactions between protons and neutrons. It refers to the strong force such as energy released by nuclear fission and nuclear fusion. In nuclear fusion, nuclei are fused, whereas, in nuclear fission, nuclei are split apart. For example, in nuclear plants, the nuclear fission of uranium takes place to generate electricity. The sun also produces energy through nuclear fusion.

The types of energy described above can be divided into two broad categories of energy: kinetic energy and potential energy.

Kinetic Energy: It is the energy that an object possesses owing to its motion such as a bullet fired from a gun, swinging pendulum, moving car, etc.

Potential energy: It is the energy stored by an object due to its position, or change in its shape, arrangement, etc. It can be gravitation potential energy that is due to the gravitation pull on an object that is located above the ground or raised to a certain height. The other is elastic potential energy that is stored in objects when they are stretched or compressed such as a compressed spring that possesses elastic potential energy.

## Units of Energy

The SI unit of energy is the joule (J) or newton-meter (N x m). The SI unit of work is also Joule as energy is the ability to do work. For example, one joule is the work done by a 1-newton force that acts over a distance of one metre.

## Law of Conservation of Energy

This law states that energy cannot be created and cannot be destroyed or the total energy of a system remains constant, however, it can be transformed into another form.

According to this law, the total energy of a system that is isolated from its surroundings remains constant or conserved. So, if loss of energy occurs in some part of this system, an equal amount of energy will be gained in some other part of the system. Although this law has not been proved yet, there is no example found that violated this law of conservation of energy. The equation used to determine the amount of energy in a given system is as follows:

Ut = Ui + W + Q

Ut : Total energy of the isolated system

Ui : Initial energy of the system

Q : Heat lost or gained by the system

W : Word done by or on the system

The change in the total energy (internal energy) of the system is given by the following equation:

∆U = W + Q

∆U = change in energy

W = work done on or by the system

Q = heat lost or gained by the system

## Law of Conservation of Energy Examples

Most of the inventions made in physics are based on the fact that energy remains conserved when it gets transformed from one form to another. There are lots of electrical and mechanical devices that work on the law of conservation of energy. Here are some common examples:

• In an electric torch, the chemical energy of the battery is converted into electrical energy, which further changes into light and heat energy. So, we cannot say that the chemical energy of the battery is destroyed, it gets converted into other forms of energy instead.
• In hydroelectric power plants, the potential energy of water when it falls on the turbines changes into kinetic energy that hits the turbines and moves them to produce electricity. The potential energy changes to kinetic energy which further changes to electrical energy.
• The wrecking ball when hanging motionless has potential energy, but no kinetic energy. When it is released, its potential energy decreases and kinetic energy tends to increase. When it hits the ground it has nearly no potential energy but has kinetic energy. Here, the potential energy of a wrecking ball changes into kinetic energy that is used for demolition purposes.
• While using a loudspeaker, the electrical energy is converted into sound energy.
• In a generator, electricity is produced due to the relative motion between a conductor and the magnetic field. Here, the mechanical energy is converted into electrical energy.
• When fuels like cooking gas, kerosene, etc., burn, their chemical energy converts into heat and light energy.
• The octane that is found in gasoline has chemical energy owing to its molecular structure. In a car engine when the combustion of gasoline takes place, this chemical energy is released to produce high-temperature and gases that move the piston and move the car forward, which gains kinetic energy.
• In living organisms also energy can change forms. For example, the potential energy stored in ATP molecules is used for the contraction of muscle cells that allow the movement of limbs. Here, the energy that we get from food, stored in ATP as a chemical energy changes to the kinetic energy of limbs.

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