A question about work

  • Thread starter jaron
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  • #1
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Main Question or Discussion Point

I have just started taking a beginner physics course and am currently studying work and its basic components [ie. W=F(d)].
now i understand the concept, but i am curious about the idea that just because something doesnt move or change its condition as a whole that the amount of work is zero.

for example: a man pushing on the side of his house with all his strength he can muster.
Now of course we all know the man wont be able to move the house, but to say no work has been done cant be right. i am talking on a very minimal level. like the changing of some of the matter of the brick or siding that he had his hands on.

just because the entire object is not effected does that mean a small part that might be affected is simply overlooked in the entire scheme of things?
 

Answers and Replies

  • #2
Nabeshin
Science Advisor
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Your confusion merely results in the difference in usage between the science and colloquial definitions of the word "work".

It is correct that if nothing moves, no work is being done! You certainly feel like you're doing work, but that is a product of your body more than anything else.

Another good example is if you pick up a 100lb box, you do work when you pick it up off the ground. If you carry it to the other side of the room while you are carrying it you do no work! Certainly the man carrying the box, who may or may not be sweating, will argue with you! But, as per the definition, no work is being done.

The "small effects" you're looking for don't really exist because structures are rigid and move as a whole (unless they break) so to do work you have to move the whole thing.
 
  • #3
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yes i understand that well enough, i just thought that there must be a more complex answer to something like this. perhaps as you get into much deeper stages of the subject.

then again, maybe not. maybe it is as simple as it seems.
 
  • #4
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yes i understand that well enough, i just thought that there must be a more complex answer to something like this. perhaps as you get into much deeper stages of the subject.

then again, maybe not. maybe it is as simple as it seems.
Recently this question was answered in the following way: the work on displacement of a body is a useful work. It is what you want. The total work spent on it by a mover is usually larger than the useful (mechanical) work.

So if you or some machine cannot move an object, it means only that the useful work equals zero but not the total work. Look at this as at the question of efficiency of a machine (or man's effort).

Bob.
 
  • #5
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ok that makes sense.

i appreciate the feedback from both of you.
 

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