Question

Define the term energy of a body. What is the SI unit of energy?

Answer 1

Energy is how much a body is capable of doing some work. It cannot neither be created nor destroyed. There are different forms of energy such as nuclear energy, electrical energy, work done, fusion energy, thermal energy. Energy can be transformed from one form into another.

Complete answer:
Energy of a body is the ability of the body to do work. Energy can exist in different types such as potential, kinetic, thermal, electrical, chemical and nuclear and many other various forms.
There are, moreover, heat and work which is then energy in the process of transfer from one body to another. After it has been transferred, energy is always changed according to its nature. Hence, heat transferred to a body might become thermal energy, while work done may be transferred in the form of mechanical energy. But the bottom line is that all the forms of energy have been associated with motion. For example, any particular body will have kinetic energy if it is in motion. Similarly, nuclear energy is a type of potential energy because it is obtained from the configuration of subatomic particles in the nucleus of an atom.
The movement of energy from one place to another is called energy transfer. Following are the four different ways through which energy can be transferred:
Mechanically – Through the action of force
Electrically – Through electrically charged particles
By Radiation – Through electromagnetic waves
By Heating –Through conduction, convection, or radiation
Law of conservation of energy: The law of conservation of energy is written as follows; “In a closed system, that is, a system that is isolated from its surroundings, the total energy of the system is conserved.” In simple words, energy can neither be created nor destroyed; it can only be converted from one form to another.
The SI unit of energy is Joule. There are other units of energy such as calorie, erg and many more. Relationships between different units of energies with its SI unit are as follows:
1J = 107 erg
1 cal = 4.184J

Note:
The SI unit of energy, which is Joule, can be defined as; when a force of 1 Newton is applied on a body and it is displaced by 1 meter, then the amount of energy that is used up in doing this work is equal to 1 joule. There are other units of energy such as kilowatt- hour and horsepower, dyne and many more.