# Kinetic Energy and Work Done

What is the first thing that comes to your mind when you see Usain bolt running? It must be that how energetic he is. But what is energy? A very general definition would be energy is a value associated with a body by virtue of its motion or configuration. Energy can be of different types as mentioned above. The energy possessed by a body by virtue of its motion is known as kinetic energy.

The kinetic energy of a moving body is given by:

K.E =$\frac{1}{2}$ mv2

• Where, m is the mass of moving body
• V is the velocity with which it is moving
• Unit of kinetic energy is Joule.

Examples of kinetic energy are moving the ball, or as large as a revolving planet.

So now we have some idea about the energy and the next thing that comes to our mind is a much commonly used term ‘work’. What is work done? Can we relate it to kinetic energy? For that, we need to recall one of the mysterious property of the universe that energy can only be transformed from one form to another. Now suppose a ball is moving with velocity ‘v’. We apply some force in the opposite direction, now the velocity becomes less than v or in other words body loses kinetic energy, So where has that energy gone? This is known as work done by force. So we can define work done by a force as energy given or taken from the system of objects.

In a more mathematical approach, we can define work done as

dW = F. ds

where, dW = work done

F  = Force

ds = displacement

So if we apply force and it results in some displacement then work is done by the force. So can we say while pushing a wall you have done some work? Let’s see using the above equation, you have certainly applied some force but since the displacement is zero hence the work done by you is zero even though you feel fatigue.