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I have seen a similar question on the site, but that was kind of different in its essence — it was aimed at asking the solution of a particular problem, while I am having trouble conceptualizing the idea of Work. Here's my understanding —

If I push a wall, it doesn't move. There is no displacement; but I DO lose some energy — a force will be applied. The wall does not move because the force that is applied is not sufficient to overcome the 'adhesive' or 'structural' forces there are at the edges of the wall and keep the wall joined to the house. Had they (and friction) not been there, the wall would have moved (though slightly). Does it not then follow that I am indeed doing work on the wall, but it simply doesn't move because other forces are doing work on it too, and my work is not enough to overcome them? It would then be reasonable to say that no net work is being done on the wall, but I see everyone saying that I, for myself, will not be doing any work at all because I will not be displacing the wall, in such a scenario.

What's wrong with my understanding?

Qmechanic
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Arjun
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  • Why not just consider the force only. There is no change in velocity of the wall and there is no net force in first place because all the force you applied is canceled by the opposite force according to the Newton's third law (https://www.physicskey.com/12/force-and-laws-of-motion). Also consider reading this article https://www.physicskey.com/14/work-and-power (and focus on the work done by the friction). If some work is done, it is done by the net force. – Saral Sep 24 '18 at 14:14

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The short answer is that you need more words in that sentence.

Is there any work done?

Is there? Where? In the whole universe?

Let's be precise.

There is no net work done on the wall

Which means that the wall is not increasing its energy. You're appliying a force on it (you), and the structure of the buuilding is cancelling it out. So no net force and no net work... on teh wall!

However, you are spending energy in overcoming those forces. What's more, your body is spending work in carrying electrons and moving your muscles. That's right, but you are a differnet system (your body is). We are talking about the wall.

In general, we say "work done on a system", not on the agent or by the agent.

FGSUZ
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  • I kinda understand what you are trying to say; but I have seen the same assertion (that no net work is done by the person pushing the wall on the wall) even without the net prefix. Is that convention? and is it that convention that you refer to in your last sentence? – Arjun Sep 24 '18 at 13:52
  • It's lazyness rather than convention haha. It means "The wall is not receiving work from the person, because it is being compensated". The wall won't move, because no dispalcement→no work. However, you'll end up tired if you keep pushing the wall, as our experience confirms. – FGSUZ Sep 24 '18 at 15:00