Energy is used to do work and make all the movements. When we eat, our body transforms the food into the energy to do work. When we run or walk or do some physical work, we use energy. Cars, planes, trains, and various machines transform energy into work. In general, anybody able to perform work is said to posses energy.
Thus, the energy of an object is defined as the capacity for doing work. Its SI unit is the joule. One joule energy is the energy required to do 1 joule of work,
The bigger units of energy are:
1 kj = 1000 j
1 mj = 106 j
Forms of Energy
There are various forms of energy. They are:
- Mechanical energy
- Heat energy
- Light energy
- Sound energy
- Magnetic energy
- Electrical energy
- Chemical energy
- Nuclear energy
1. Mechanical energy
The energy possesed by the state of the body (either rest or motion state) is called the mechanical energy. It again has two forms. They are
- Kinetic energy
- Potential energy
1. Kinetic energy
The energy possesed by a body by the vitrue of its motion is called the kinetic energy. Mathematically, the kinetic energy of a moving object is defined as the half the product of its mass (m) and the square of the velocity of that object (v).
Therefore, kiinetic energy, \(KE=\frac12mv^2\) ; where m is the mass and v is the velocity
The examples of bodies having kinetic energy are:
- A ball rolling on a surface
- A bullet fired from a gun
- Water in motion
- A falling body
- Moving car
- A running man, etc
2. Potential energy
The energy possessed by a body by the virtue of its position is called potential energy. Mathematically, the potential energy of a body is defined as the product of its mass (m), acceleration due to gravity (g), and its height from the ground (h)
Therefore, potential energy (PE) = mass × acceleration due to the gravity × height
∴ PE = m × g × h
The potential energy may be gravitational or elastic energy stored in spring for example.
Examples of the bodies possessing energy are:
- A stretched rubber of catapult
- A stretched bow
- Water stored in a dam
- A stone at a height, etc.
2. Heat energy
Heat is a form of energy produced due to the random vibration of the molecules of the body. It flows from the body at a higher temperature to a body at a lower temperature. It gives us the sensation of warmth. Heat energy is used to do various types of work such as cooking food, making our body warm, boiling water, running engines, etc. It is also produced due to the combustion of coal, petrol, mineral oil, chemical reaction, nuclear reaction, etc.
3. Light energy
Light is a form energy which gives us the sensation of vision. We get light form the sun, a burning candle, a glowing bulb, etc. The sunlight trapped by chlorophyll is used by green plants to prepare their food. So, due to the sunlight, all living things can survive on the earth.
4. Sound energy
Sound is a form of energy produced due to the vibration of the molecules of a body. It gives us the sensation of hearing to our ears. It can produce disturbance in a medium, through which it propagates. So, it is also regarded as a form of energy.
5. magnetic energy
The energy possessed by a magnet with help of which it can show the attractive and directive property is called magnetic energy. With the help of magnetic energy, a magnet can attract magnetic substances like iron, nickel, cobalt, etc. So, magnetic energy is used to separate iron dust from soil, iron dust from eyes, and in factories, it is also used to lift heavy loads.
6. Electrical energy
It is a form of energy produced due to the change in the number of electrons in a body or the flow of electrons through a conductor. Electricity is the most versatile form of energy that can be easily changed into other forms like, heat, sound, light, etc. Nowadays electricity is used to run electrical appliances like TV, radio, refrigerator, bulbs, vehicles, cookers, etc.
7. Chemical energy
The energy released by a body when it undergoes a chemical change or reaction is called chemical energy. Our food consists of chemical energy, when it gets oxidized with air then it gets converted into heat energy. It is used to perform various activities in animals' and plants' bodies. Similarly, the chemical energy stored in fuel when burnt with oxygen releases in the form of heat. It is used to run vehicles.
8. Nuclear energy
The tremendous amount of energy released by changing the nucleus of one atom into another is called the nuclear energy. They heavy atoms are unstable and they break into simpler nuclei. THis preocess is called the nuclear fission. Similarly the lighter nuclei get combined and form a heavier nucleus and the process is called nuclear fusion. In both of these processes, enormous energy is released and this energy is called the nuclear energy. Atom bombs and hydrogen bombs are based on the nuclear energy. The nuclear energy is also used to generate electricity.
Law of Conservation of Energy
The law of conservation of the energy states that, " energy can beither be created nor be destroyed but can bee changed from on form to another".
Lavoisier in 1774 stated that matter can neither be ceated nor be destroyed. This was called the law of conservation of mass. But according to Albert Einstein, mass can be converted into energy and vice-versa. Thus, the laws of conservation of mass and energy have become one, which is called the law of conservation of mass-energy.