All Questions
Tagged with classical-mechanics work
211
questions
67
votes
15
answers
22k
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Why is ascending some stairs more exhausting than descending?
I have been asked this question by school kids, colleagues and family (usually less formally):
When ascending a flight of stairs, you exchange mechanical work to attain potential Energy ($W_\text{...
- 831
52
votes
4
answers
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What's the real fundamental definition of energy?
Some physical quantities like position, velocity, momentum and force, have precise definition even on basic textbooks, however energy is a little confusing for me. My point here is: using our ...
- 36.4k
20
votes
3
answers
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Conditions for a force to be conservative
Taylor's classical mechanics ,chapter 4, states:
A force is conservative,if and only if it satisfies two conditions:
$\vec{F}$ is a function of only the position. i.e $\vec{F}=\vec{F}(\vec{r})$.
The ...
- 1,295
18
votes
2
answers
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Conceptually, what is negative work?
I'm having some trouble understanding the concept of negative work. For example, my book says that if I lower a box to the ground, the box does positive work on my hands and my hands do negative work ...
- 181
14
votes
5
answers
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Proof of conservation of energy?
How is it proved to be always true? It's a fundamental principle in Physics based on all of our currents observations of multiple systems in the universe. Is it always true to all systems? Because we ...
- 677
13
votes
1
answer
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The role of the virtual work principle
Lanczos' masterpiece "The Variational Principle of Mechanics" has, on page 76, the following statement:
Postulate A (virtual work): The virtual work of the forces of reaction is always zero for any ...
- 4,013
12
votes
2
answers
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Can a force in an explicitly time dependent classical system be conservative?
If I consider equations of motion derived from the principle of least action for an explicitly time dependent Lagrangian
$$\delta S[L[q(\text{t}),q'(\text{t}),{\bf t}]]=0,$$
under what circumstances (...
- 8,513
9
votes
5
answers
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D'Alembert's principle and the work done by constraint forces in Atwood's machine
From what I understand, constraint forces do no work because they are perpendicular to the allowed virtual displacements of the system. However, if you consider an unbalanced Atwood machine, in which ...
- 483
8
votes
11
answers
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Is it more work to put more (apparent) effort to get the same outcome?
I was taking my dogs for a walk yesterday evening when this question occurred to me.
The two dogs were pretty enthusiastic about the walk and wanted to run on ahead, so the leads were taut and they ...
- 257
8
votes
4
answers
602
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Is there a fundamental reason not to define the work vice-versa
My question arises from something which has never been really clear: in continuum mechanics, why is strain energy defined as:
$$W=\int_\Omega \underline{\underline{\sigma}}:\mathrm{d}\underline{\...
- 734
8
votes
2
answers
2k
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Intuition behind Work
I have a doubt in understanding the intuition behind the concept of work. First of all, I think this isn't duplicate, I've searched on the site, and the closest thing I've found was this post which is ...
- 36.4k
7
votes
1
answer
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A Question about Virtual Work related to Newton's Third Law
In describing d'Alembert's principle, the lecture note I was provided with states that the total force $\mathbb F_l$ acting on a particle can be taken as,
$$\mathbb F_l=F_l+\sum_mf_{ml}+C_l,$$
where $...
- 190
6
votes
2
answers
1k
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What is the physical intuition behind this energy conservation theorem?
I'm reading Quantum Theory for Mathematicians, by Brian C. Hall. Although the book is about Quantum Mechanics, it's chapter 2 is actually about Classical Mechanics, in which I encountered the ...
- 163
5
votes
2
answers
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Why does the work-energy theorem need to include internal forces?
Can anyone kindly explain me why work energy theorem must also include internal forces?
The proof of work energy theorem is derived from Newton's laws of motion, but Newton's laws of motion don't ...
- 399
5
votes
3
answers
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How the definition of work is derived from Noether theorem?
I cite the following phrases from an answer to the Phys.SE question Why does a force not do any work if it's perpendicular to the motion?
...an alternative would be to treat the work-energy ...
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