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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Was Joule's experiment able to show: thermal energy = $mgh$

Is my understanding of this experiment correct? There is the quantity $MC\delta \theta$ associated to the heat which I think is not an absolute value to be compared with $mgh$ since the $\delta ...
2
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0answers
195 views

Conservation of Mechanical Energy [closed]

I am currently trying to tackle the problem: A 2.0 kg bundle starts up a 30° incline with 125 J of kinetic energy. How far will it slide up the plane if the coefficient of friction is 0.30? ...
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2answers
189 views

Not so simple problem using momentum, energy and angular velocity…?

I have an object in free space (no gravity) with angular momentum $ = \omega_i $, and some velocity vector $=\vec{V_i}$. To simplify we will say it has a mass-less rigid rod length $ = \ell $, ...
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2answers
198 views

almost same mass, same distance, different energy needs

Imagine a car, driving 10 km at constant speed in 6th gear. There will be a measurable fuel consumption. Now imagine the same car driving 10 km again at a constant speed (same as above) in the 1st ...
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3answers
596 views

Does unitarity imply conservation of energy?

Not too long ago, someone began to discuss the thinking and motivation behind the Lagrangian and its formalism for the Newtonian framework and an intuitive understanding of such formalism. Somehow, it ...
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2answers
190 views

How does energy transfer between B and E in an EM standing wave?

I'm trying to understand how an electric field induces a magnetic field and vice versa, its associated energy, as well as relating it to my understanding of waves on a string. Using a standing wave ...
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1answer
810 views

Where do the photons mediating the electromagnetic force come from?

The electromagnetic field is mediated by photons (energy quanta). Its range is infinite, the interaction only weakens quadratically with distance due to the area of an expanding virtual sphere. Where ...
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2answers
1k views

The physical observation of the conservation of energy?

Aside from Noether's Theorem, how do we know energy is conserved? Energy is the capacity of a system to do work. It's the number that tells me how much "force" a system can apply over a distance. For ...
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1answer
2k views

Explicit time dependence of the Lagrangian and Energy Conservation

Why is energy(or in more general terms,the Hamiltonian) not conserved when the Lagrangian has an explicit time dependence? I know that we can derive the identity: $\frac{\partial ...
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12answers
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Where does the extra force generated by a lever come from?

Given an object being pulled down to earth by a force of 1000 lb: If a machine were to lift it off the ground for me, and I grabbed on to the rope before it was released, there is no way in the world ...
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2answers
21k views

Perfect elastic collision and velocity transfer

So my teacher told me that when you have two identical balls in a perfectly elastic collision, the first ball A will collide with B and afterwards A will stop and B continue. Why is this? Doesn't ...
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2answers
7k views

Finding max height of a mass launched by a spring?

I have the following problem on my homework. The actual problem has numbers, but I figure using symbolic notation will help me understand the concept in the long run. A block of mass $M$ is launched ...
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1answer
152 views

Understanding Where I Went Wrong in a Linear Conservation Problem

I have the following physics problem. In the figure below, a stationary block explodes into two pieces L and R that slide across a frictionless floor and then into regions with friction, where they ...
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1answer
2k views

Physics transformation energy [closed]

A 15kg child slides down a 2.3m -high playground slide. She starts from rest, and her speed at the bottom is 2.1m/s . What is the change in the thermal energy of the slide and the seat of her pants? ...
2
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2answers
13k views

How to find the compression of a spring attached to an object [closed]

I am having some trouble figuring out the equation needed to solve this problem. A 3.0-kg block slides along a frictionless tabletop at 8.0 m/s toward a second block (at rest) of mass 4.5 kg. A ...
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1answer
184 views

Superfluid Fountain

I was wondering how a super fluid fountain can flow indefinitely without violating energy conservation.
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4answers
2k views

Gravitational Potential Energy (GPE) to Kinetic Energy (KE) transfer in Satellite Orbits

I am stumped by a mundane A Level Physics question (teacher of physics here obviously a bit short of practice!). My colleagues and I are stumped and were wondering if any one could help us. It ...
2
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1answer
98 views

Thermodynamics and Energy conservation in the Scope of the Universe

According to the 2nd law of thermodynamics, no system can be a 100% efficient. Looking at the universe as it's own system, is it an exception to the rule (a system that doesn't lose any energy)? If ...
2
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1answer
324 views

Does the concept of a wormhole violate the law of mass-energy conservation?

If my understanding of wormholes is correct, anything that moves into a wormhole can be transported from one region of space-time to another. Consider a situation where an object of mass $m$ in space ...
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1answer
4k views

Heavy vs Light Particle Ideal Gases

Assume there are two ideal gases. The first is made of a light particle, and the second is made of a heavy particle. The two are of the same amount, in the same volume container, and at the same ...
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3answers
199 views

Mass-Energy Equivalence

I've asked before, but I'm still confused as to what the mass energy equivalence implies. I've taken an introductory course in relativity, so I only covered special relativity. From what I gather, all ...
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1answer
304 views

Does the big bang violate the conservation of energy? [duplicate]

It is a fact that a thing is existing now because it had already been created. So why don't we take this to account to redefine law of conservation of energy.
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2answers
1k views

How to understand Feynman's reasoning about perpetual motion?

I'm studying Feynman's Lectures on Physics, and I'm not really understanding his reasoning here: Consider weight-lifting machines $\overline{}$ machines which have the property that they lift one ...
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2answers
3k views

Where does tidal energy come from?

Kind of an odd, random question that popped into my head. Tidal energy - earth's ocean movement, volcanism on some of Jupiter's moons, etc. - obviously comes from the gravitational interaction between ...
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1answer
2k views

Are principle of Conservation of energy and principle of conservation of momentum consequences of Newton's laws?

It is known that principle of Conservation of momentum and principle of conservation of energy are two fundamental principles of physics.But in RP Feynman's Lectures of physics, in the chapter of ...
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5answers
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Proof of conservation of energy?

How is it proved to be always true? It's a fundamental principle in Physics, that is based on all of our currents observations of multiple systems in the universe, is it always true to all systems? ...
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2answers
132 views

What happens to gravitational waves after arbitrarily long propagation?

Given that some systems may radiate energy in the form of gravity waves, and that gravitational waves weaken proportionally to the distance travelled, what would happen to the waves that never hit ...
0
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1answer
79 views

We create systems with different values of Energy? [closed]

I understand that Energy is a conserved quantity in a system. A number, that's always the same to the system. However, don't we determine such a number? I mean, we can create systems(Or study them ...
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0answers
511 views

Making an equal amount of positive and negative energy?

I was wondering if it would be possible to create an amount of positive energy out of a vacuum, in addition to an equal amount of negative energy, thus not violating the first law of thermodynamics, ...
2
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0answers
66 views

What quantum states can be measured using entanglement?

I have been reading about quantum entanglement, and I was wondering what quantum states can be "sent" using entanglement. I know you can measure the spin of one of the particles, and know the spin of ...
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1answer
610 views

Numerical schemes, time integration algorithms and energy conservation

What does it mean when someone says a numerical scheme or a time integration algorithm is "energy conserving". How can a numerical scheme "gain" or "lose" or "conserve" energy apart from the numerical ...
2
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4answers
4k views

Does light loses its energy when it passes through denser medium?

I know it does not because it emerges out of denser medium at 300,000 KM per second, but according to $E=mc^2$ and given that speed of light decreases inside denser medium with refractive index ...
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1answer
3k views

Gentle slope vs steep slope

Take for example a slide of 3m tall. Would an object (starting from rest) sliding down a gentle slope have a lower speed than a steep slope? (Note: Height of slide is the same,disregard friction.) ...
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2answers
7k views

Why can't we destroy energy?

From a wikipedia article: In physics, the law of conservation of energy states that the total energy of an isolated system cannot change—it is said to be conserved over time. Energy can be neither ...
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2answers
2k views

Nuclear reactions and energy conservation

How are nuclear fission and fusion compatible with the law of conservation of energy? During fission $He$ splits into 2 hydrogen atoms along with enormous amount of heat energy and hydrogen also ...
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2answers
7k views

What prevents this magnetic perpetuum mobile from working?

As a child, I imagined this device, which may seem to rotate indefinitely. I have two questions. Is this perpetual motion machine already known? If it is, could you please give some references? What ...
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3answers
1k views

Is it possible to deduce the conservation of angular momentum from the conservation of energy?

Is it possible to deduce the law of conservation of angular momentum from the law of conservation of energy? If possible, by what sense the conservation of angular momentum has the status of law, if ...
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1answer
842 views

Speed of a falling pencil [closed]

If you balance a pencil of length $d$ on its tip, and let it fall, how do you compute the final velocity of its other end just before it touches the ground? (Assume the pencil is a uniform one ...
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2answers
263 views

Conservation of Energy and CP violation

In classical mechanics there is Noether's theorem: If a system has a certain symmetry there is a related conserved quantity. Energy conservation is a result of a system being time invariant. This is ...
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5answers
744 views

If I replace all my lights with LEDs will my heating costs increase?

A number of nations are passing bills to phase out incandescent light bulbs. The thinking is that the tungsten filament is an inefficient method of turning electricity into light, the rest of the ...
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1answer
904 views

Life and Death, and Energy Conservation

Humans are born and they die. When we are born, is energy created? Or is it just some amount of energy that our mother gives us? Doesnt she take this energy from the surroundings? If so, then when we ...
2
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1answer
548 views

Which direction does the electron move?

If my phone is charging that means it's mass increasing by this Youtube video. Now if an current is flowing from the power station to home, does it mean that electron is flowing from house to the ...
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0answers
46 views

Nuclear Fission and Fusion [duplicate]

I've read several other answers on here, but I still don't understand. Why do both fission and fusion release energy? I know the masses drop, but then why do the masses drop on both? Fusion is taking ...
0
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3answers
938 views

Conservation of Angular Momentum, as related to a flywheel

Trying to work out some pesky flywheel dynamics for a project I'm working on, would love some for your assistance to better understand the underlying concepts. For a given flywheel (thin-walled ...
2
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0answers
76 views

Do cosmologically redshifted photons violate energy conservation? [duplicate]

I understand that, due to the Doppler effect, different frames of reference moving at different velocities relative to each other will measure different photon frequencies and hence energy. The ...
0
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1answer
115 views

An electron emits a photon and the core is pushed (recoiled) back!

I have come across a problem which is a homework indeed, but i tried to pack this question up so that it is more theoretical. What I want to know is: If I am allowed to write energy conservation for ...
3
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1answer
2k views

Lagrangian and conservation of energy

If Lagrangian of the motion is $$\mathcal{L}=\frac{1}{2}m\left(a^2\dot\phi^2+a^2\dot\theta^2\sin^2\phi\right)+mga\cos\phi,$$ how can I show that total mechanical energy is conserved? I've read ...
12
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2answers
2k views

Compressed Spring Dissolving in Acid

This is just an interesting question a friend's uncle asked me that I was somewhat annoyed I couldn't answer. When a material dissolves in acid there is a chemical process that causes the changes in ...
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2answers
1k views

Conditions for Conservation of energy law

In two-dimensional motion, which conditions are needed to be satisfied so the conservation of energy law holds? (for example, simple pendulum motion)
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136 views

Motion on a smooth surface

A particle of mass $m$ is moving on the inner side of smooth circular cylinder of radius $R$ whose $Oz$-axis is vertical and directed downwards. The particle started its motion from the $x$-axis with ...