# Am I correct in rejecting this example of No-work force?

I have seen this example in several books.

The work done by a porter in carrying a luggage on head while walking on a horizontal force is $0$ as the gravitational force is at $90^0$ with the horizontal plain.

Now,I cannot accept it as I think that the gravitational is not causing the displacement.So,we cannot relate this force with another displacement caused by a different force (here,the muscular force of the porter).

So,am I correct?

Thanks for any answer!!

• Forces don't cause displacements. Forces cause changes in velocity. – march Nov 16 '15 at 17:33
• @march-It may not be directly related but a subtle factor for displacement... – tatan Nov 17 '15 at 7:42