list them activity 11.2 work and energy
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11. Work and Energy
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Chapter 11
NCERT Book with important points highlighted and links to past board questions
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Work and Energy
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?
11.1 Work
What is work? There is a difference in the way we use the term ‘work’ in day-to-day life and the way we use it in science. To make this point clear let us consider a few examples.
11.1.1 Not much ‘work’ in spite of working hard!
Kamali is preparing for examinations. She spends lot of time in studies. She reads books, draws diagrams, organises her thoughts, collects question papers, attends classes, discusses problems with her friends, and performs experiments. She expends a lot of energy on these activities. In common parlance, she is ‘working hard’. All this ‘hard work’ may involve very little ‘work’ if we go by the scientific definition of work.
Answer:
Work is referred to as the displacement of an object when a force (push or pull) is applied to it while energy is referred to as the capacity to do the work. It exists in various forms like potential, kinetic, chemical, thermal, nuclear, electrical energy and so on.