## Energy

Subject: Science

#### Overview

The capacity of a body to do work is called the energy of the body. Conversion of energy from one form to another form is called transformation of energy. Energy can neither be created nor be destroyed but can only be changed from one form to other. This note provides information about different types of energy.
##### Energy

The capacity of a body to do work is called the energy of the body. The SI unit of energy is joule (J). Energy can exist in various forms. Different forms of energy are:

1. Mechanical energy: Energy by the virtue of which a body can do some mechanical work directly, is called mechanical energy. The common forms of the mechanical energy are:

• Kinetic energy:The energy possessed by a body due to its motion is called kinetic energy. Kinetic energy (K. E) of a body having mass m, and velocity v, is equal to equation That is, K. E = mv2

• Potential energy:The energy possessed by a body due to its position or configuration is called potential energy. Potential energy (P.E) of a body is P.E = m x g x h

Where, m is a mass of the body, g is the acceleration due to gravity and h is height.

2. Electrical energy: A form of energy created by the movement of electrons is called electrical energy. I.e. hydropower, generator, etc.

3. Light energy: Light is also form of energy that makes things visible. We use light in the different process like lightening the houses, running industries, etc. Plants use energy to make food.

4. Heat energy: Heat energy is obtained by burning combustible substances like coal, gas, kerosene, firewood, etc. We use heat energy to keep warm and to cook food.

5. Sound energy: Sound energy is also a form of energy which is produced by vibrations. We hear the sound when the vibrations travel through the air around it to vibrate.

6. Chemical energy: The energy stored in the matter such as the energy stored in food and fuels, is chemical energy.

7. Nuclear energy: The neutrons and protons exert an attractive force on each other when present in the nucleus. The energy associated with them is called nuclear energy.

8. Magnetic energy: The energy can also be produced by a magnet. A magnet is the source of energy. Electricity can be produced with the help of the magnet. It is more powerful and also can be used to lift a heavy weight.

#### Transformation of energy

Conversion of energy from one form to another form is called the transformation of energy.

When a candle burns, chemical energychangesinto light and heat energy. When a fan is switched on, it converts an electrical energy into mechanical energy. Similarly, when a lamp glows, it changes electrical energy into light and heat energy. These examples show that one type of energy can be changed into another type.

Examples:

1. A steam engine changes heat energy into mechanical energy.
2. Solar car converts solar energy into mechanical energy.
3. A microphone converts sound energy into electrical energy.

#### Conservation of energy

Energy can neither be created nor be destroyed but can only be changed from one form to other. This is called the principle of conservation of energy.

##### Things to remember
• The capacity of a body to do work is called the energy of the body. The SI unit of energy is joule (J). Energy can exist in various forms.
• Conversion of energy from one form to another form is called transformation of energy.
• This is called the principle of conservation of energy.
• It includes every relationship which established among the people.
• There can be more than one community in a society. Community smaller than society.
• It is a network of social relationships which cannot see or touched.
• common interests and common objectives are not necessary for society.
##### Where Does Energy Come From (clip)
 s.n magnetic energy chemical energy 1 It is produce from magnet. It is due to a chemical reaction. 2 Electricity can be produced with the help of magnet. This energy is released in the form of electrical energy. 3 It is used in radio, telephone, and telegraph etc. Store in matter such as the energy store in food and fuel.

The energy possessed by a body due to its position or configuration is called potential energy. For example, a raised stone has potential energy and can do the work and a stretched rubber band has potential energy because of their stretched condition.

A flying bird possesses both potential and kinetic energies as it is at a certain height above the ground and moving with the certain velocity.

A man is standing at the rest on a moving car does not possess kinetic energy.

Chemical energy is form of energy that the food contains.

Kinetic energy depend on following factors:

• The kinetic energy of a body is directly proportional to the mass of the moving body.
• The kinetic energy of a body is direct proportional to square of velocity of body.

Conversion of energy from one form to another form is called the transformation of energy. Examples of conservation of energy are:

1. A steam engine changes heat energy into mechanical energy.
2. Solar car converts solar energy into mechanical energy.
3. A microphone converts sound energy into electrical energy.

Energy can neither be created nor destroyed but can only be changed from one form to other. This is called the principle of conservation of energy.

\begin{align*} \text{mass}\:(m) &= 65\: kg \\ \text {velocity} \: (v) = 10 km/hr = \frac {10\times 1000 m}{1 \times 60\: \text {min}\times 60\: \text {seconds}}\\ &= 0.2777\: km/hr \\ \text {kinetic energy} (K.E) &= ?\\ \text {We know} \\ K.E. &= \frac {1}{2}mv^2 \\ &= \frac 12 \times 65 \times (0.277)^2 \\&= 2.49 \: \text {joules} \\ \end{align*}

\begin{align*} \text {Given,} \\ \text {mass} \:(m) &= 10 kg \\ \text {height from the ground} \: (h) &= 10\: m \\ \text {acceleration due to gravity} \:(g) &= 9.8 ms^2 \\ \text {potential energy}\: (P.E.) &= ? \\ P.E. &= m\times g\times h \\ &= 10 \times 9.8 \times \: 10 \\ &= 980\: \text {joule} \\ \end{align*}