[alshaymah]

If you pick a heahy suitcase and hold it off the ground for a while. It makes you more tired thatn if youran one hudered yards. Yet if work involves movement of things.In physical sense you are doing no work whatsoever. Can you resolve this paradox?

[ebaines]

Since work = force x distance, no work is done on the suitcase after you have lifted it to the steady position. From its perspective the suitcase doesn't care if you grow tired or not - as far as it's concerned it may as well be sitting on a table. But your body does do work while you are holding the heavy object - your heart pumps more blood than when you are at rest, so the heart is definitely doing work. It is applying force to your blood stream, moving the blood through the arteries, veins, etc. So the organs in your body are doing work, although not on the suitcase.

Another example: think about a hovering helicopter that is stationary with respect to the ground. While stationary it does no work on its cargo, but it clearly requires fuel to keep it aloft. It expends energy to move air downward with enough acceleration to counteract its own weight. So clearly the helicopter engine does work, although the cargo has no work done upon it.

[asterisk_man]

There is no paradox. There is a difference between the common definition of work "application of force" and the technical definition of work "force * distance".

[Capuchin]

It's like when someone says that "evolution is only a theory", it's a clash between technical language and common language.