The statement that a property of a system does not change if the system is isolated.
Questions tagged [conservation-laws]
3101 questions
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Intuition for continuity equation
Suppose, for example, we have an equation,
$$\frac{\partial \rho}{\partial t}=-\nabla \cdot\vec J$$
which we can apply to show conservation of electric charge. How can we interpret this intuitively?
user147033
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3 answers
Feynman's layman proof of local charge conservation
https://www.youtube.com/watch?v=r_IfV9fkBhk#t=10m55s
And it ends at 16 minutes. I have a great love for Feynman's explanations but right now I seem to have failed to understand exactly how his example proved charge is conserved locally. The…
AntiElephant
- 203
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Photon absorbed, identical Photon re-emitted
I believe I frequently see it stated that a photon is absorbed and an identical photon is emitted.
How can the energy in equal the energy out, with no loss?
user40910
- 87
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Conflicting Derivations of the Continuity Equation
Hello fellow students of physics,
I'm beginning my study on 'Stellar Structure and Evolution' and in the book I'm studying the author(s) begin(s) by stating simplifying assumptions for a first model of a star: gaseous, non-magnetic, non-rotating and…
2
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Conservation law of equation involving Hilbert transform
I am trying to confirm a conservation law I cam across in a paper (Janssen 1983 "On a fourth-order envelope equation for deep-water waves" Journal Fluid Mechanics), and am having difficulty.
In particular, I'm trying to confirm the conservation of…
Nick P
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Conservation of momentum for ball to triangular prism physics
A ball of mass m1 is hitting a resting triangular prism of mass M with an unknown velocity of v1. After the hit the prism is moving forward with a velocity V and the ball up with the velocity V1a.
The surface of the prism making contact with the…
Keidi
- 11
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1 answer
Feynman Mass vs. Charge Movement
In The Character of Physical Law, Feynman presents a brief proof that charge conservation must be local. I had some confusion over local vs. global conservation, but thought I understood after reading the discussion in this question.
Later on in the…
andars
- 179
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Continuity equation - water mass conservation
I have a problem to understand a passage in the article "Modeling the dynamics of pressure propagation and diameter variation in tree sapwood" that you can find here:…
Donald Webb
- 11
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What do the recent vacuum tests mean for the believability of NASA's EM Drive?
NASA has been testing an EM drive for a while. Although the initial results appeared positive, the scientific community was skeptical because these results would violate conservation of momentum. Much criticism was directed at the fact that thermal…
Casebash
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How is the momentum conserved in the case of recombination in direct bandgap semiconductor?
In the case of a direct bandgap semiconductor, the recombination of an electron and a hole generates a photon that has energy equal to the bandgap of the semiconductor, accounting for energy conservation. But in this case, as the electron and hole…
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Probability current density in a momentum eigen state seems counter-intuitive
The physical significance of probability current density (PCD) is usually given as a local conservation of probability. The time rate of reduction of probability at a point is accompanied by a local outward PCD.
In a momentum eigen state, say…
som
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How do symmetries of nature give rise to the conservation laws?
In my physics textbook, the following points are given:-
The Law of Conservation of linear momentum emerges from the homogenecity of space.
Isotropy of Space gives rise to the Law of Conservation of angular momentum.
Homogenity of time gives rise…
Mriganka Parasar
- 859
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2 answers
Isolated system and external forces
I have problem of understanding fully "isolated system",
if i imagine a car moving at a constant speed ,can I say that is isolated system although an interna force (car's engine) cancel out an external force ( friction)
Gio lou
- 11
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In the law of conservation of linear momentum why does the force that body A exert on body B equal the rate of change of momentum of body B?
In the law of conservation of linear momentum why does the force that body A (first) exert on body B (second) equal the rate of change of momentum of body B? And why does the force that body B exerts equal the rate of change of momentum of body A?
