Science

# Work, Force and Energy – Class 5

A work is said to be done when we use force to push or pull objects around us. Now, to do this work we need certain amount of energy. Without energy we cannot do any work. Thus, work, force and energy are all inter-related to each other. In this topic for Class 5 we will learn more about work, force and energy.

#### What is Work?

A work is said to be done when a force applied on an object causes it to move a certain distance in the direction of force. Let see some example where work is said to be done.

• Walking or running
• Pulling or pushing an object from one place to another place
• Playing any sports in a playground
• Using staircase to carry an object

A man pushing a trolley

Let see some other example where work is not being done.

• Lying still on the ground
• Holding an object but not moving
• Pushing against a wall
• Reading a book while sitting on a chair

A man holding bags but not moving

Thus, even if you are reading a book for hours, or holding heavy weight, it will not be considered a work because there is no movement. Similarly, if you are trying to push a wall by applying your total force against it but no work is done because the wall does not move. Thus, work is said to be done only when the object on which the force is applied moves a certain distance in the direction of force.

#### Force

Force is a push or a pull acting on an object. A force can be used not only to move an object to a certain distance but also to stop it. A force can change the direction of an object also.

#### Energy

Energy is defined as the capacity or ability to do work. Work and energy are related to each other. There is always a change or transfer of energy when a work is done. Thus, for every work we need some amount of energy. But how do we get this energy? We get energy from the food that we eat. Carbohydrates and fats in the food gives us this energy. These are also called energy-giving foods. Rice, wheat, butter, ghee, sugar, etc. are energy giving foods.

#### Types of Energy

Mechanical energy, electrical energy, solar energy, light energy, heat energy and wind energy are some types of energy.

Mechanical Energy: The energy that an object possesses due to its position or motion is called mechanical energy. It is also known as the sum of potential energy and kinetic energy of a body or system. This you will learn in higher classes.

For example, a moving car possesses mechanical energy due to its motion. A moving baseball also possesses mechanical energy due to both its high speed and its vertical position above the ground.

Electrical Energy: Electrical energy is an energy that is caused by moving electric charges. These energy are generated mostly at power stations and supplied to our homes to run electrical appliances like television, fan, bulb, refrigerator, washing machine, computer, etc.

Solar Energy: The sun is full of energy and and solar energy comes from sunlight that reaches earth. Thus, the energy that is generated from the rays of the sun is called solar energy. Solar energy can be stored and used to heat buildings and to make electricity.

Solar Panel using sun light to generate electricity

Heat Energy: We get heat energy from many sources. Sun is the natural source of heat energy. We also get heat energy from burning of fuels such as Liquefied Petroleum Gas (LPG) used in gas cylinders. This energy is then used for cooking foods.

Wind Energy: Energy generated from moving air is called wind energy. This energy is converted into electrical energy by windmills. A windmill is a structure with large blades on the outside which when turned by the force of the wind generates electrical energy.

Wind Mill

#### Renewable Energy and Non-renewable Energy

Renewable energy is energy produced from sources such as sun, water and wind and last for a long period of time. Solar energy, hydro energy and wind energy are examples of renewable energy.

Energy that are produced from sources such as coal, petroleum and natural gas that do not last for a long period of time are called non-renewable energy. These type of energy are perishable in nature. That means, coal, petroleum and natural gas will not last forever. Therefore, we must use these energy judiciously and carefully.