# Questions tagged [conservation-laws]

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

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0answers
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### Compression of airbags

I am currently creating a simulation of a rover landing on mars. Part of the landing would include the rover being dropped to surface of mars whilst surrounded by airbags. I understand that using ...
2answers
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### Rocket's momentum

It is well known that to give a liftoff a rocket, we use the momentum principle: The momentum of the gases emitted by a rocket and the rocket's momentum is equal to zero. So why is it not enough to ...
0answers
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### Block slides down frictionless wedge on frictionless surface. Find accelerations of the blocks

I am working on a physics problem where a small block of mass $m$ slides down a wedge-shaped block of mass $M$ with an angle $\alpha$ to the horizontal that rests on a frictionless horizontal surface. ...
5answers
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### Does the movement of a passenger change the velocity of an aeroplane?

I encountered a problem in my physics textbook today. An aeroplane of total mass of 50,000kg is travelling at a speed of 200m/s. If a passenger of mass 100kg then walks toward the front of the ...
3answers
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### How is momentum conserved in the case of a ballistic pendulum collision?

To my knowledge, momentum is conserved when net external force equals zero. In the case of a block $m_1$ attached to a string hitting another block $m_2$, there must be a net force on $m_1$, which ...
0answers
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### Finding symmetry from conserved quantity (reversed Noether's theorem) [duplicate]

Is Noether's theorem reversible? For example, given some conserved quantity, can you find the underlying symmetry which leads to the conserved quantity?
3answers
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### How does an accelerating mass on a ring interact with the ring?

In outer space, imagine a mass $m$ on a ring with mass $M$. The small mass is given a velocity $v$ after which it moves without friction on the ring. Initially, the velocity of the center of mass (COM)...
1answer
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### Why can't we use conservation of angular momentum to solve this question since this whole system is isolated?

A solid rubber wheel of radius $R$ and mass $M$ rotates with angular velocity $\omega_0$ about a frictionless pivot. A second rubber wheel of radius $r$ and mass $m$ also mounted on a frictionless ...
2answers
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### If everyone on Earth jumped at the same time, is it possible to steer the Earth?

Newton's third law states that in every action, there is a equal and opposite reaction. When we jump, we exert a force on the ground and the resultant force upwards propels us up into the air. However,...
1answer
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### How can Hawking radiation maintain the balance of matter and antimatter?

If hawking radiation simply reduces the mass and emits electromagnetic radiation, how can the balance of matter / antimatter be maintained? Couldn't you use some of that $E = mc^2$ energy you would ...
1answer
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### How is energy conserved in blueshifting?

I am having trouble understanding the conservation of energy in the scenario below. A photon of $\lambda_1$ is emitted by a source and then absorbed by object 1 in space. Object 1 can be considered ...
3answers
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### Friction during rolling

I have four doubts regarding friction during rolling. Does slipping mean zero angular velocity, or is it just the $v$ velocity not being equal to $\omega r$? If a wheel is initially given the ...
1answer
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### How to understand the Fresnel relation $1+R=T$? [closed]

From the perspective of energy conservation, we are familiar with the relation $T+R=1$ (Set the incident wave amplitude as 1, $T$ and $R$ are Fresnel transmission and reflection coefficient, supposing ...
1answer
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### Energy conservation in systems with discrete time

Numerical simulations of classical particle dynamics usually break energy conservation due to discretization of time. Is there any explicit numerical scheme that does not break energy conservation (...
1answer
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### 1D Elastic Collision with restitution coefficient

I have an exercise about a 1D collision with a certain restitution coefficient, that is: $$e = \frac{|u_1-u_2|}{|v_1-v_2|}$$ One must calculate the velocities of the 2 colliding masses after the ...
1answer
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### Conservation of Energy with Chemical and Kinetic Energy of Moving Body

A rocket is moving relative to the earth such that it has $E$ joules of kinetic energy. The rocket contains fuel with $E$ joules of chemical energy. The mass of the fuel is negligible in comparison to ...
1answer
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### Conservation of momentum: One moving car hitting another stationary one. Does the target always move forward?

Consider an isolated system with two cars of any mass, a ground with friction, and Earth. Both cars are free to move on the ground. One car (Car #1) is moving towards the other stationary car (Car #2)...
1answer
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### What is the significance of the term 'isolated system' in law of conservation of charge?

I did not understand why charge can only be conserved in an isolated system. Kindly elucidate.
3answers
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### Why is angular momentum $mvr$ and not $mvr^2$ or $mvr^3$?

We know angular momentum $L = mvr$, where $v$ is the velocity in the direction perpendicular to the distance from the source to the object whose $L$ we are trying to measure. My question is why $L$ ...
8answers
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### If electrons can be created and destroyed, then why can't charges be created or destroyed? [duplicate]

I read on Wikipedia that electrons can be created through beta decay of radioactive isotopes and in high-energy collisions, for instance when cosmic rays enter the atmosphere. Also, that they can be ...
1answer
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### Forces in an elastic 1D collision [closed]

Let's say I have block A (5kg, a = 10 $\frac{m}{s^2}$) and block B (20kg, a = 20 $\frac{m}{s^2}$). When they collide together elastically, the forces exerted on each other should be the same by Newton'...
4answers
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### Conservation of Charge

We know that universe is all about charge conservation mass conservation and energy conservation. Charge on a system can be measured by comparing it with charge on a standard body, positive and ...
2answers
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### Symmetry principles and analogous Noether's theorem for stochastic systems

In the case of Newtonian mechanics, taking a variational or Lagrangian or Maximum principle (MP) view, one can obtain the conservation laws (energy, linear momentum and angular momentum) by combining ...
1answer
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### Adiabatic Invariant when forcing is at the natural frequency of a classical simple harmonic oscillator

Consider a simple harmonic oscillator of unit mass, natural frequency $\omega_0$, given by the Hamiltonian \begin{align} H_0(q,p)=\frac{1}{2} \left[ p^2 + \omega_0^2 q^2 \right] \ . \end{align} Now ...
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### Kinetic energy produced in an explosion

If there is a train moving at 2 m/s with a cannon attached to it loaded with a ball, and then the ball is launched from the train, how would one find the kinetic energy produced by the explosion if ...