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Energy and Power

Work-Elementary Idea

Work and energy are the two terms used very often in our day-to-day lives. We often call someone very energetic, if the person is capable of doing a lot of work. In physics also, energy and work are very closely related and their meanings are not very different from the way we use them in our daily lives. What is the relation between work and energy?

Energy is defined as the ability to do work.

You know what work is.

When a force displaces an object along its direction, we say the force does a work.

Therefore, a body has the ability to do work, if it possesses some energy. Without spending energy, a body cannot do any work. If we think about it a bit, then we will see that to apply a force, some amount of energy has to be spent. From this, we can also conclude that if work is done on a body, then some energy gets transferred to the body. For example, if we lift a stone to a certain height, then a work is done on the stone to lift it against the force of gravity. For that, we use energy stored in our muscles. Again, the work is stored as energy in the stone by virtue of its position. Therefore, when the stone is released from the height, the stored energy gets released.

Thus, we can conclude that energy is required to do some work. On the other hand, if some work is done on a body, then the spent energy that gets stored in the body in turn becomes capable to do some work. This is called work−energy relation.

Consider the following day-to-day activities: reading, speaking, singing, writing, thinking, etc. We require energy to perform these activities, which we derive from the food we eat. Did you know that actually no work is involved in performing these activities? Do you think that a weightlifter does work while standing with weight over his head, as shown in the given figure?

Even if you push a wall with the maximum force that you can apply, the wall will not move. It will be interesting for you to note that even in this case, you are not doing any work at all! Do you know why?

Work is not done in all the above activities because there is a basic difference between the term work and the term which we use for our daily activities.

Scientifically, work is defined as the work done by a force that causes a displacement in an object.

Whenever a body moves, it covers a distance. The straight line that joins the initial and final positions of the body is called its displacement.

Distanc…

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