Questions tagged [energy-conservation]

The law of conservation of energy, which states that the amount of energy in a system is constant. For questions about Earth's environment, see the climate-science tag instead.

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Collisions and conservative and non-conservative forces

How can I prove or argument that if in a collision there are only conservative forces acting on the system then the kinetic energy of the system is conserved, and if there are non-conservative forces ...
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Energy conservation in center of mass frame [closed]

I came across the following problem in which the ring of mass m is given an initial velocity $v_0$ and a particle if mass $3m$ is attached to the other end. We need to find the maximum deviation of ...
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Spring block system on a rough surface [closed]

Suppose we have a given a block of mass m connected to a spring of spring constant k and kept over a rough horizontal surface having coefficient of friction u.Initially the spring is compressed by d (...
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1answer
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Is the height relative to the ground or the pitcher's bat? [closed]

"A ball of mass 100 g is hit vertically upwards with a bat. The bat exerts a constant force of 15 N on the ball and is in contact with it for a distance of 5 cm. How high will the ball go?" ...
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Does gravitational potential energy always decrease?

Assuming a system of two particles with no external force acting on it,the two particles would come together due to mutual gravitational forces (ignoring electromagnetic forces). Since gravitational ...
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6answers
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Why does a ping pong ball bounce higher when it is dropped together with a cup of water?

Setup: an official ping pong ball is floating inside a party plastic cup filled with clean water, which is then dropped from a certain height onto a soft mat. Observation: the ping pong ball shoots up ...
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2answers
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What is the external force during rebound of a ball?

Consider the situation when a ball hits a plane surface at an angle of incidence $\theta$ with speed $u$ and rebounds with the same angle. One can notice that there is a change in momentum in this ...
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3answers
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How does an up quark decay into products more massive than itself?

According to https://en.wikipedia.org/wiki/Up_quark the up quark can decay into a down quark plus a positron plus an electron neutrino. The problem is that the mass of the by-products is greater than ...
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1answer
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Eternal looping water tap

If i have a container like this (filled full with water): and I unplugged the small tap, would the water pressure be big enough to blast the water to the right side of the container and cause an ...
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2answers
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Is it practically possible to make an air conditioner more energy efficient?

I have had this thought for a long time that an air conditioner is connected to an exhaust device that pumps hot air away. However theoretically it should be possible to channel that air flow into ...
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2answers
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Gravitational potential energy conversion

A unit mass is brought closer to the Earth from infinity, with zero acceleration. The potential energy decreases the kinetic energy does not change, so where is the energy going? Which form of energy ...
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3answers
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Are two interacting electrons in an isolated system?

From your point of view, two electrons are initially at rest. In time, they repel one another, leading to an increase in both of their kinetic energies. If they are isolated from the rest of the ...
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Kinetic energy vs. momentum [closed]

I am confused about how the law of the conservation of (kinetic) energy and the law of conservation of momentum can both hold true. If we observe a certain collision, then depending on the final ...
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2answers
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What is the direction of the velocity $v=\sqrt{2gy}$ vector? Is it tangential? If so, why?

I was trying to obtain the brachistochrone as a function of time, and I failed several times because I wrongly assumed that the $v=\sqrt{2gy}$ vector points downwards (vertical vector). However, in ...
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What's the meaning of $\Delta E-W_{nc}=0 $?

Suppose a system of particles is subject to internal forces, some of which are conservative and some of which are non-conservative. Let $\Delta E$ be the change in mechanical energy of the system as ...
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1answer
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Why can't we solve this question by using conservation of energy? [closed]

A block of mass $m$ is attached to one end of a light string which is wrapped on a disc of mass $2\,m$ and radius $R$. The total length of the slack portion of the string is $l$. The block is released ...
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1answer
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Energy conservation and electromagnets

I was reading here the paragraph about electromagnets. It is written that: "Electromagnets are usually in the form of iron core solenoids. The ferromagnetic property of the iron core causes the ...
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1answer
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Can they reach the point? [closed]

According to the figure, pendulum $OA$ is released from position $A$ and it collides with another pendulum $OB$ at point $B$ and after the inelastic collision, they continue their oscillation. (Mass ...
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Is there a way to verify that energy of a body is directly proportional to mass, without using the definition?

How would I go about verifying that the energy a body possesses, is directly proportional to its mass to the first degree, without using the definition of work? How could I show this fact without the ...
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Does this implementation of applying an impulse off-center violate conservation of energy?

I am currently working with a 2D-physics-engine, that allows applying an impulse p⃗ at a point x⃗ relative to an objects center ...
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1answer
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Are all orbits of the conservative pendulum homoclinic?

I don't understand this statement: "The homoclinic orbit is characterized by $E = mgl$. When $E < mgl$, the pendulum is tracing other orbits." If energy is conserved, then $E_0 = E$ ($E$...
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1answer
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What is the total energy of a object if i throw it so far from the earth that it doesnt move towards earth? It seems there is energy loss

Let us assume that i throw a object A with velocity V_A. Then it reaches certain height H_A. At that point it has total energy which is equal to its potential energy and it comes down converting PE to ...
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1answer
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Yo yo motion and energy conservation

I am struggling with balancing energy in a yo-yo. So, we have a yo-yo (massless string wrapped around solid cylinder). It is allowed to fall through a distance $h$ without rotation. The loss in ...
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Kinetic energy converted to what for the case of a magnetic braking of a disc?

To what the kinetic energy is converted for a rotating disc which is braked by a magnetic field? The question is a bit difficult, because the obvious answer about eddy currents is not the final answer ...
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2answers
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How can we transform energy conservation laws on inclined plane? [closed]

Suppose a inclined plane Now in normal projectile problem we can normally apply energy conservation laws but in this case since this is a inclined plane we have to transform the conservation laws now ...
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What is the second conserved Quantity of the Pendulum?

Consider the problem of a classical pendulum whose state can be described by a function $\theta(t)$ where $\theta$ is measured from the line directly below. We then have that our pendulum's $\theta$ ...
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1answer
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Do waterfalls conserve momentum? If so, how?

I understand that waterfalls conserve energy, given the fact that the top of a waterfall possesses gravitational potential energy, and as the water is falling from top to bottom, this potential energy ...
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Applying energy conservation to two sphere system with leaking charge

Two identical charged spheres suspended from a common point by two massless strings of length l, are initially at a distance (x<<l) apart because of their mutual repulsion. The charge begins to ...
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2answers
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Why do peaks and troughs of a wave cancel each other out? And why peaks and peaks or troughs and troughs add up?

I have thought that the cancellation of peaks and troughs is a consequence of Newton's third law of motion that equal and opposite forces cancel each other out. Or it has something to do with ...
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1answer
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Why isn't the total potential energy of an elastic system equal to zero?

I'm studying FEM. My book says that "the work of internal forces is equal the the work done by external forces" and it states it in an equation Wi=We. But then it somehow starts discussing ...
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1answer
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Does energy conservation imply time invariance?

This is similar to this question: Is the converse of Noether's first theorem true: Every conservation law has a symmetry?. However, the answer given there is very technical and general. I am only ...
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1answer
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Solving Particle in a Box using Newtonian Mechanics [closed]

so I'm trying to solve the one dimensional particle in a box problem known from quantum physics in a classical context. So according to Wikipedia (see picture on the right) we would get a particle ...
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1answer
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Weight is storage for energy, right?

Since weight is storage for energy, the light vehicle will have a slight advantage on the flat ground due to low stress applied on wheels meaning less friction pulling the vehicle back. When though, ...
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1answer
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Speaker on bicycle - would it propel the rider forward?

You strap a super powerful speaker on your back, blast it on max volume. Would it propel you forward?
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How can global warming occur in spite of Energy Balance?

The Greenhouse Gas Theory maintains that an increase in carbon dioxide will cause a corresponding increase in Earth's temperature. But this temperature increase will cause an increase in the flow ...
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1answer
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How does an expanding universe and a constant-density vacuum energy not violate energy conservation? [duplicate]

As per the title. I'm probably thinking too naively in a classical way, but intuitively it seems to me that: the presence of vacuum energy at fixed density throughout all space and, an expanding ...
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3answers
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I want to know how law of conservation of energy holds in the generation of electricity in dams? [closed]

Basically law of conservation states that input energy is equal to the output energy. But i was wondering that in case of generating electricity in dams no input energy is required. As the dam only ...
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1answer
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Buoyancy perpetual motion machine with compressors at top and decompress-or at bottom [closed]

a link to consideration about the perpetual motion machine [] diagrams and working out are included above. the assumptions are set to minimise engineering challenge and face perpetual motion machine ...
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David Morin Problem 5.54- Tetherball

My thought process was such- on changing the length of the string, the only two independent parameters that could change were the angle $\theta$ and tangential speed of particle$\ v$ (as radius$\ r$ ...
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1answer
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Dissipative energy intuition

Over the time i have been doing physics i have noticed a pattern related to energy that gets dissipated in systems which come to equilibrium after a certain time has passed. please hear me out with a ...
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1answer
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Question about a chapter in Feynman's book [closed]

I was reading six easy pieces by Feynman, and I had reached the section on the Conservation of energy This chapter was defintly one of the harder ones so far, especially considering that his ...
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1answer
122 views

'Perpetual motion' paper by George Biddell Airy

Airy wrote a paper (maybe deceptively) titled On certain Conditions under which a Perpetual Motion is possible (Cambridge Philosophical Transactions, December 14, 1829). Alternative site (in more than ...
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Isolated systems and 'internal energy'

I am familiar with isolated systems. They don't interact with the environment and no energy transfer takes place across the boundary of the system. My textbook says, In an isolated system, if ...
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Foundations of conservation of 4-momentum in special relativity [duplicate]

From first principles, how can we argue that four-momentum is a conserved quantity in processes like particle collisions and decay? I understand that since the external spatial force is 0, the ...
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2answers
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Conservation of momentum and work

Consider the following scenario: I am alone in space with a ball. I threw the ball at a certain speed such that i am propelled backwards (like a rocket is) as to conserve momentum. Now, since my ...
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Are velocity fields in energy conserving systems necessarily irrotational?

Let's assume that we consider a bunch of particles (e.g. water or air) and we describe their velocity using a vector field $\vec v(\vec x, t)$. Moreover, let's assume that there is no external ...
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Mechanical energy conservation for different chosen systems

I studied work-energy theorem and the equation for mechanical energy conservation yesterday. I’m not able to understand how to identify forces when choosing a system (which force is which). This is ...
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How did the adiabatic process equations combine to form this new one?

Compressing and cooling air in a Coolgardie Safe, then decompressing I'm a 10th grader so it would help to explain how, in the answer to the link above, $$T_{cool}\left(\frac{V_{final}}{V}\right)\...
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2answers
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If a sphere is rolling down a friction-less incline surface, does it not roll? [duplicate]

I'm solving a problem where a ball rolls down a hill, but the friction between the ball and surface is 0. So it obviously slips, but does it only slip? As in does it not roll at all? Or does it slip ...
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1answer
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Bungee jumping: why does using the law of conservation of energy give me a different $k$ than solving for $k$ when the net force is 0? [closed]

I tried solving the following problem: "A 62.0kg bungee jumper jumps from a bridge. She is tied to a bungee cord whose unstretched length is 12.0m and falls a total of 31m. Calculate the spring ...

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