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In the last few chapters, we have discussed,
  • different ways of describing the motion of objects and
  • the cause of motion and gravitation.
Another important concept that encourages us to understand and explain many natural phenomena is ‘work’, which is closely related to energy and power.
In this chapter, we shall discuss work and energy.
Various machines are also developed to do activities to achieve the goal.
What do they need for their work (Process or activity)?
Why do some engines require fuel like petrol and diesel?
Why do living beings and machines need energy?
If we answer the above questions, we get an overview of Work and Energy.
Food is necessary for all living beings. They have to do many basic activities to withstand. We describe such activities as life processes. The energy required for all these processes comes from food.
We require energy for other activities such as playing, singing, reading, speaking, writing, thinking, jumping, cycling, running, etc.
The more the work is complex, the more it requires energy.
Animals too get involved in activities such as jumping and running. To fight for their lives or to find food or a secure place to live,  Also, some animals are engaged to lift weights, carry loads, pull carts or plough fields. Energy is required for all such activities.
Machines are also needed fuels to get the energy to complete their works.