INTRODUCTION
In the previous few chapters, we have talked about ways of describing the motion of objects, the cause of motion, and gravitation. Another concept that helps us understand and interpret many natural phenomena is ‘work’. Closely related to work are energy and power. In this chapter, we shall study these concepts. All living beings need food. Living beings have to perform several basic activities to survive. We call such activities ‘life processes’. The energy for these processes comes from food. We need energy for other activities like playing, singing, reading, writing, thinking, jumping, cycling, and running. Activities that
are strenuous require more energy.
Animals too get engaged in activities. For example, they may jump and run. They have to fight, move away from enemies, find food, or find a safe place to live. Also, we engage some animals to lift weights, carry loads, pull carts, or plough fields. All such activities require energy.
Think of machines. List the machines that you have come across. What do they need for their working? Why do some engines require fuel like petrol and diesel? Why do living beings and machines need energy?
Source: This topic is taken from NCERT TEXTBOOK