WHO DOES WORK WHEN YOU WALK?

WHAT YOU NEED TO KNOW?

- The basics of work done by a force and how to draw a free-body diagram of a body

Now, let's draw a free body diagram of a man walking. 

The only force acting on the man is at the feet where friction acts in the forward direction and does the work, but that's where the misconception settles in. 

We know that the formula of the work done by a force is -

We know that friction is an example of a contact force. This means that the friction is only acting on the feet when it is in contact with the ground. However, the foot does not move when it is in contact with the ground. Hence, the friction force does zero work during the entire process of walking. 

Also, the Force of Gravity and Normal reaction from ground act at normal to the surface and hence don't contribute in the work done. 

So, the question is that which force is acting which does work while we walk?

The force which does the work is a force which can't be easily shown on a free body diagram. It is the MUSCULAR FORCE of the person walking which does the work, but it has an arbitrary direction and acts on multiple points of the body. That's how while exercising the body uses our internal stored energy (which we get from food) is used up. This also explains the reason why we feel hungry after a good workout or a long walk as our internal energy reserves get depleted.

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