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3 votes

Does doing work on system increase or decrease its internal energy?

If $\Delta V$ is negative due to compression of the gas, then the sign of the work is positive and the internal energy will increase. The convention used here is that the sign of the work done on a ...
Matt Hanson's user avatar
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1 vote

What are the forces that do work when a spring between two masses pulls inwards?

There is no kinetic energy change in the second system (1,2, spring). So there is no net work done, so no need to ask which external forces that do the work. The constituent particles of the system do ...
Steeven's user avatar
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0 votes

Drawbacks of Quasi-Static process for lifting a block

And why do we need a quasi-static process to explain Potential Energy in the first place? We don’t. A quasistatic process is not required to explain potential energy. It is only a necessary condition ...
Bob D's user avatar
  • 73.7k
1 vote

Can siphons improve the efficiency of hydroelectric dams?

No, you cannot gain any efficiency. Remember the bernoulli equation: $P_1 + \frac12\rho v_1^2 + \rho gh_1 = P_2 + \frac12\rho v_2^2 + \rho gh_2$ If you have water at rest at $P_{atm}$ on the top, and ...
Pato Galmarini's user avatar
2 votes
Accepted

Work Done by kinetic friction in Circular Motion

In circular motion, your total displacement $$\oint \mathrm{d}\vec{s}$$ is zero, correct. But for work, you are not integrating just the displacement $\mathrm{d}\vec{s}$, but the quantity $\vec{F}\...
CompassBearer's user avatar
0 votes

Does work differ between inertial frames?

This will help: "The kinematical roots of dynamics", S. R. Madhu Rao, Am. J. Phys. Abstract: "Whenever the total kinetic energy of an isolated collection of interacting bodies changes, ...
SennGorSan's user avatar
16 votes
Accepted

Areas with anti-parallel gravity in classical physics

If we let the $y$-axis point upwards then OP's 2D gravitational field is $$\vec{g}~=~ \begin{pmatrix} 0 \cr g~{\rm sgn}(x)\end{pmatrix}.$$ It has a non-zero curl $$(\vec{\nabla}\times \vec{g})_z~=~2g\...
Qmechanic's user avatar
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5 votes

Areas with anti-parallel gravity in classical physics

The potential that yields your provided force field is discontinuous. One possible choice would be $$V(x,y) = \begin{cases} gy & x\leq 0 \\ -gy & x>0 \end{cases},$$ which has a dicontinuity ...
Refik Mansuroglu's user avatar
1 vote

Energy Transfer and Work in Action-Reaction Forces

Because doing work on something doesn't make you gain kinetic energy. Now I have said this multiple times on this site, and will continue: Bringing the human body into physics never, ever, helps. It ...
JEB's user avatar
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1 vote

Voltage: work to move a charge, or difference of electric potential?

In the diagram below the red dashed circle with the negative charge at its centre is an equipotential with the electric field lines produced by the negative charge at right angles to the circle. As ...
Farcher's user avatar
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1 vote
Accepted

Voltage: work to move a charge, or difference of electric potential?

it will take work to move the positive charge from point A to point B, as I must counteract the vertical component of the electric force and so on. You are quite correct that the distance to the ...
John Rennie's user avatar
0 votes

Why is work done by force $+mgh$ in the situation of throwing something up?

But the work done by the force that brings it above to point B is $+mgh$. I dont think its necessary. That will mean that the force making it move up is $+mg$ but it can also be something else. If ...
Bob D's user avatar
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0 votes
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In layman’s language what is the difference between stopping potential and work function?

Work function is the minimum energy required to liberate an electron from a solid to the space immediately outside the solid. Stopping potential is the electric potential difference between two ...
mike1994's user avatar
  • 978
0 votes

Why is work done by force $+mgh$ in the situation of throwing something up?

System: particle. Two forces acting on the particle, gravitational attraction due to Earth, magnitude $mg$, downwards and external force exerted by you, magnitude $mg$, upwards. If the particles rises ...
Farcher's user avatar
  • 97.9k
-1 votes

Why is work done by force $+mgh$ in the situation of throwing something up?

I don't quite understand the question. You have a force $\vec{F}$ acting on the object to take it from A to B. This force is an external force, which goes against the force of gravity, and also this ...
JL14's user avatar
  • 67
1 vote

Why is work done by force $+mgh$ in the situation of throwing something up?

You are right, the work applied is not necessarily equal to $mgh$. To see this, let's look at energy conservation: $$K_0+U_0+W_{\text{n.c.}}=K_f+U_f$$ where $K_0$ and $K_f$ are the initial and final ...
BioPhysicist's user avatar
  • 57.2k
4 votes

Strange calculus involved in work and power

The correct formula for work is $$ \Delta W = \int P d t = \int \vec{F} \cdot \vec{v} \,dt $$ Now, if $\vec{F}$ is constant, then we can take it out of the integral and write $$ \Delta W = \vec{F} \...
Prahar's user avatar
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1 vote
Accepted

Work performed by hydrostatic pressure

With a little less math, the power of a stress distribution $\mathbf{t}_n$ over the boundary of a volume $V$ is $$P(t) = \oint_{\partial V} \mathbf{t}_n \cdot \mathbf{u} \ ,$$ being $\mathbf{u}$ the ...
basics's user avatar
  • 10.6k
0 votes

Work performed by hydrostatic pressure

My intuition is that we are looking at a special case of Stokes' theorem, since we are relating surface integrals to volume changes. To this end, it seems clear enough to me that the differential ...
creillyucla's user avatar
0 votes

Why the work done by surrounding on the piston is same as average work done by surrounding on the gas inside the cylinder?

But it's the work done on the PISTON. I will only address this statement, as some of your other statements are not clear (at least to me). There is no net work done on the piston unless (1) it ...
Bob D's user avatar
  • 73.7k
1 vote

The conservative force

While @basics has the math right, I understand your question is about the physical interptetation. To answer this, we must understand what a force field is, since the definition of the rotation ...
paulina's user avatar
  • 1,897
1 vote

The conservative force

An example might be the best way to see it. Set up some electrodes that create a horizontal electric field. Make it so the field strength is proportional to height. This is a non-conservative field. ...
mmesser314's user avatar
  • 41.1k
1 vote

The conservative force

Remark the curl it's the measure of the rotation of the vector field around a specific point Before answering your question, I'd replace (local) "rotation" with (local, or elementary) &...
basics's user avatar
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