# Questions tagged [conservation-laws]

The statement that a property of a system does not change if the system is isolated.

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### Why doesn't pulling in your arms on a rotating stool violate conservation of energy? [duplicate]

From what I understand, pulling in one's arms on a rotating stool would decrease the radius, thus decreasing the moment of inertia. If we decrease the radius enough to halve the moment of inertia, we ...
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### Accessible States in the Ergodic Hypothesis

According to Wikipedia, the ergodic hypothesis is the assumption that all accessible microstates are equiprobable over a long period of time. My question is about the precise meaning of "...
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### Are Van Der Waals Forces related to the Van der Waals Equation?

In a physics class, I learned about Van Der Waals forces that allow geckos to stick. Do they have any relation to the Van Der Waals Equation relating gas pressure to temperature and volume?
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### Why do internal forces not affect the conservation of momentum?

How is momentum conserved? I know that the condition is that no external resultant force should act on the interacting objects. But how is the momentum conserved if the objects surfaces touch and ...
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### Law of Conservation of Time? [closed]

So, it may or may not seem to be stupid, but if we think that there is a person named John who travels back in time by any means, and he met his past lets say him small John then the past small John ...
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### Stopping Distance in Conservation of Momentum Investigation

In a set of old textbook materials from Merrill Physics from the mid 90s, there is a page on Fitch Inertial Barriers put near construction zones. Three cars are going to collide into a set of these ...
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### Consequence of diffeomorphisms invariance in General Relativity

Let's consider a theory with gravity and matter field(s) $\Phi$. The action of this theory is the following: S[g,\Phi] = S_g[g]+S_m[g,\Phi] = \frac{1}{16\pi G}\int_Md^4x\sqrt{-g}R+\...
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### Equation in Field Quantization Greiner

Hello, I dont understand the red part. Shouldn't it have minus instead? Sorry for lack of formatting, I only have a phone.
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### Newton's third law and cannons

A cannonball firing from a cannon is often given as an example of Newton's third law. The explanation goes like this: The cannon exerts a force on the cannonball and thus the cannonball exerts an ...
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### Different symmetries or no symmetries in string theory?

I was reading the book "A Fortunate Universe" by Geraint Lewis and Luke Barnes and something caught my attention: At page 195 the authors say that universes with different symmetries could ...
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### Calculating final velocity of two colliding protons?

In an isolated system of two colliding protons [ say, proton1(p1) and proton2(p2)]; initially p2 is at rest, and p1 is moving with uniform horizontal velocity $\vec{u_1}=a \hat{i}$ m/s. First way of ...
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### Angular momentum vectors

Hi I am trying to learn the concepts of angular momentum but I don't understand why in the formula for torque the radius from the line of action of the force is regarded as a vector surely distance is ...
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### What term describes the trajectory space splitting behavior when parametrizing a pendulum?

So I was thinking about this post I made earlier: What is the second conserved Quantity of the Pendulum? In which a pendulum appears two have significant properties. It's Kinetic Energy and its Phase. ...
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### Differential with respect to constant in Canonical Tranformation

I'm reading canonical transformation from Classical Mechanics by Goldstein. It says, considers a situation in which the Hamiltonian is a constant of the motion, and where all coordinate $q_i$ are ...
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### Kepler's Second Law: conservation of the energy or of the angular momentum?

Reading from example the old question, Angular Momentum and Kepler's Second Law Considering that now I not remember the proof because starting from the angular moment conservation of $L$ we have ...
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### Why does an oscillating mass does not produce gravitational waves (in contrast with an oscillating electric charge)? [duplicate]

I would like to gain insight about this question. I have read it is related with the conservation of momentum, but cannot really differentiate it from the oscillating charge. The monopole radiation ...
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I'm currently in my second year of master. From what I understand, in QFT, Noether's first theorem implies that for any continuous symmetry (i.e. associated to a $n$-dimensional Lie group $G$, $n\geq ... 0answers 38 views ### Constants of motion [duplicate] For any system performing any kind of motion with$n$degrees of freedom, are$2n-1$integrals of motion and also$2n$constants of motion always present? If yes, then is there always a symmetry for ... 4answers 2k views ### What is the reason for this apparent paradox caused by a massless spring with a locking mechanism? Imagine that a ball of mass$m$is launched at a block, which also has mass$m$. Attached to the block, facing the ball, is a massless spring with a massless board at the end. Alternatively, we can ... 1answer 103 views ### Does the uncertainty principle say that conservation of momentum is violated in quantum mechanics? [duplicate] The uncertainty principle of Heisenberg says that the uncertainty in the position of a particle multiplied by the uncertainty of the momentum of a particle is always more than or equal to$\frac{\hbar}...
Assume a rocket is being vertically accelerated in a homogeneous gravitational field. In the reference frame of the rocket, the burnt fuel is being exhausted downwards with a velocity of $\Delta u$. ...
I was doing a physics problem, and it had asked me to find the maximum $K_e$ loss, but I don’t understand why the loss is maxed when the objects stick together (the collision is inelastic).