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.

Filter by
Sorted by
Tagged with
1
vote
2answers
49 views

Why are certain quantities so fundamental to physics

Apart from having a qualitative description of quantities such as momentum, work and energy, why are these quantities considered so fundamental? What is the reason to define them in the first place? ...
0
votes
2answers
42 views

Buoyant force of tides and conservation of energy

Imagine an electric power generator in a form of a floating object moving up and down and utilizing the buoyant force of sea tides. Can anyone explain how it doesn't violate the principle of ...
1
vote
2answers
26 views

Mechanical enegy conservation

Is the mechanical energy conserved when the speed is constant ? What if we have a charge that entered an electric field due to an external force -which is making a dynamic equilibrium with the ...
0
votes
2answers
58 views

Will momentum be conserved in case of electrostatic force?

If a charged particle approached another particle of same charge held by some external force, then by coulomb's law the particle will start electrostatic repulsion. Thus coming to a closest distance ...
-2
votes
0answers
20 views

Verify Conservation of energy for variable gravitational field [duplicate]

Remember we can verify conversation of energy in gravitational field when we take g to be constant When we leave body from H At a point h As potential energy is mgH -mgh Kinetic energy. ...
0
votes
1answer
68 views

Verify conservation of energy in gravitational field [on hold]

Remember we can verify conversation of energy in gravitational field when we take $g$ to be constant When we leave body from $H$ At a point $h$ As potential energy is $mgH -mgh$ Kinetic energy $=mv^...
0
votes
3answers
48 views

How does an object gain energy when it enters a potential field?

Conservation of energy says total change in energy is $0$. Let's assume a small object is in outer space (maybe like a football). It moves towards a planet (assume planet has no atmosphere for ...
1
vote
2answers
38 views

Is Kinetic energy always conserved in an elastic collision/impact?

While working out through some problems I encountered this problem : A ball moving with a velocity $v$ hits a massive wall moving towards the ball with a velocity $u$. An elastic impact lasts for ...
1
vote
1answer
34 views

What's wrong in my approach towards solving this problem?

This is the problem that I have to solve: The figure shows a block $A$ of mass $6m$ having a smooth semicircular grove of radius $a$ placed on a smooth horizontal surface. A block $B$ of mass $m$ ...
0
votes
2answers
65 views

Is the information in the universe increasing?

As per what I know high entropy state requires more information to describe it as they are more random. Our universe is constantly moving towards high entropy state. So is the information needed to ...
-1
votes
1answer
28 views

$\mu_k$ of surface from experimental vs theoretical acceleration [on hold]

I have an air track at a slight angle with a glider. Final velocity is determined, and from that a is calculated, and from a, I have approximated g. I am trying to find $\mu_{k}$ between the track and ...
-1
votes
1answer
36 views

Is mass slowly destroyed when force of gravity is applied? [duplicate]

This may seem like a far fetched idea, but consider this system. Imagine a simple system of just the Moon orbiting around the Earth, creating low tides and high tides with its gravity. Now imagine ...
6
votes
2answers
104 views

Can I use the expansion of the universe to create or destroy energy?

Imagine I have a setup like this: (The objects are not attached to each other. The red objects are much heaver than the black one, and the setup is balanced.) This setup has a non-zero ...
0
votes
1answer
48 views

Axe bounces all the way back

Here's something I can't quite understand: The video Woman Dodges Death in Axe Throwing Accident shows a woman throwing an axe at a wall, and the axe bounces back all the way — how's that possible? ...
0
votes
1answer
26 views

Energy of Rod about pivot

Consider a rod, with mass $m$ and length $l$, that is fixed about a pivot point at one of its ends. Now imagine that we flick the rod so that the end of it attains a velocity of $v_{0}$. Now, if we ...
-1
votes
1answer
44 views

Friction and energy conservation [closed]

A curved surface is shown in figure . The portion BCD is free of friction. There are three spherical balls of identical radii and masses. Balls are released from rest one by one from A which is at a ...
38
votes
4answers
9k views

Is this cheap “air conditioner” able to cool a room?

My parents bought this "air conditioner", but I am very skeptical that this can cool a room, or even cool anything. I doubt that it even has a cooling element, I suspect that it is just a fan + ...
0
votes
2answers
38 views

Virtual particles, conservation of energy & the fabric of space [duplicate]

Do virtual particles take energy from the fabric space and when they annihilate in the split second they distribute that energy back to space, therefore abiding by the law for the conservation of ...
0
votes
2answers
30 views

Energy conservation with Newtonian gravitational fields

Suppose we have a mass $m$ in space, and we then introduce a bigger mass $M$. both have no kinetic energy initially. $M$ & $m$ attract, and move towards each other gaining some kinetic energies ...
0
votes
3answers
73 views

Differing results from different conservation laws

I am currently studying for the GRE Physics subject test by working through published past tests. My question is about problem 44 from the test GR8677: $44.$ A uniform stick of length $L$ and ...
0
votes
0answers
27 views

Confinement energy and energy conservation

When particles are confined, they gain confinement kinetic energy. Where does this energy come from in terms of energy conservation?
1
vote
2answers
38 views

Where does the energy go when punching a ball in the air causing it to “float”?

Here is a link to a video of a people punching a ball so it appears to float: https://www.youtube.com/watch?v=v7wqrUFREK0 When the arms are continuously punching the ball, it does not change the ...
-1
votes
1answer
113 views

The Zero Energy Hypothesis and its consequences for particle creation and dualist interactionism

Most attacks on the possibility of dualist interaction cite the conservation of energy as a definitive objection. I have attempted to investigate the validity of this objection, and have found a ...
1
vote
1answer
57 views

Conservation of Kinetic Energy?

A rod is hinged in a vertical plane. If we throw a ball at the rod's lowest point with some velocity, and they undergo elastic collision, can the total mechanical energy be conserved? What about the ...
0
votes
2answers
37 views

Conservation & Flow of Energy in Circuits

Before I ask my question, it's important that you know how I understand the underlying physics of circuits, so you could point out any misunderstandings or incomplete thoughts. A battery creates an ...
1
vote
2answers
47 views

Solving a lever problem using Newton's laws, without energy conservation?

Context: I have no background in physics, and I'm trying to understand the role of the concepts of energy, momentum and other invariants/symmetries in physics. In particular, I'm trying to get a feel ...
2
votes
2answers
65 views

Does all energy of moving car converts to thermal energy?

I argue with my friend and cannot say that he is wrong although I feel it somehow. But I don't have good arguments against him. I want to know who is right and why. The problem is Let's imagine we ...
0
votes
0answers
51 views

What makes Earth's orbital motion and the motion of a pendulum both periodic? [duplicate]

What is the commonality which makes the motion of a bob attached to a spring , motion of a pendulum with any amplitude or that of the earth around the Sun all to be periodic despite very different ...
0
votes
1answer
53 views

How does gravitational potential energy work in Relativity?

According to relativity, the universe is expanding, at an accelerating rate. Far away planets and stars will soon leave our observable universe. But as planets and stars leave our observable universe, ...
-1
votes
0answers
45 views

What was the source of energy at the moment of big bang? [duplicate]

We know that our universe emerged from the point of singularity, right after the big bang, 13.7 billion years ago. Singularity is the point of infinite density and gravity i.e. all energy and mass ...
4
votes
3answers
111 views

Where does the energy used to fight gravity go?

Imagine the following scenarios: A. We have a spaceship at x distance from a star. It faces directly away from the star, and fires its engines such that it ...
2
votes
4answers
67 views

Do air conditioner power ratings violate the 2nd law of thermodynamics?

I just got a new AC rated at 6000 BTU and wanted to determine its power consumption. Some research on AC conventions quickly reveals that 6000 BTU really means 6000 BTU/h, where BTU is a measure of ...
0
votes
1answer
41 views

Lavoisier law of mass conservation vs. conservation of energy

Lavoisier law states that for any isolated system, mass must be conserved over time. Also, Einstein's equation $E = mc²$ shows energy-mass equivalency. So, since mass must be conserved and energy ...
0
votes
0answers
19 views

Chemical reactions in fluids

The equations of motion of ordinary relativistic hydrodynamics are derived by considering conservation equations of the energy tensor and particle number current, where constitutive relations relate ...
2
votes
1answer
52 views

Do emitted photons have a well defined frequency or just a spread as per HUP?

I have read this question: Conservation of Energy in photon exchange between two atoms where Kurshal Shah in a comment says: As per the energy-time uncertainty relation, the emitted photon ...
2
votes
2answers
45 views

Conservation of energy when external force is applied [duplicate]

I have heard that an isolated system is where no energy and no mass is exchanged with outside the system. Does that imply that no external force can be applied to an isolated system? Why? For example,...
2
votes
1answer
62 views

Mechanics of a particle problem (potential energy vs. work approach)

I'm trying to reconcile two methods of approaching a problem, see picture below: Disregarding the angle of the surface and any friction, calculate the velocity $v$ of a particle pulled back a ...
0
votes
2answers
52 views

Conservation of Energy in photon exchange between two atoms

Consider a hydrogen atom, A, in the first excited state placed at a small distance from another hydrogen atom, B, in the ground state. Now, when A drops down to the ground state, it emits a photon ...
1
vote
1answer
117 views

Trying proving that energy and momentum are conserved in every inertial frame

I'm trying to show, using Lorentz transformations, that if relativistic energy and momentum are conserved in $S$, then they are conserved in $S'$ too. A wrong proof Let's suppose I know that in ...
0
votes
0answers
33 views

Does Larmor precession of a magnetic spin produce a (time-averaged) electrostatic near-field?

I have been wondering whether or not applying a magnetic field to a material containing magnetic spins could produce an electrostatic-like field as a result of a Larmor precession of the embedded ...
1
vote
1answer
74 views

Does the Breit–Wigner formula indicate “violation” of energy conservation?

In the quantum mechanical derivation of Breit–Wigner formula, for example, in the particle physics book of Martin & Shaw, we assume if the resonance particle $X$ is in an initial energy state with ...
1
vote
1answer
61 views

How to measure (heat) energy used?

Before I start with my question, would like to highlight - the last time I delved into this topic was 13 yrs back during my schooling courses. But the enthusiasm never died. Coming back to topic - I ...
0
votes
2answers
54 views

Gathering energy from an object that casts no shadow [closed]

In various books, movies, video games, etc., a common element that appears is an object that does not cast a shadow. Usually this lack of a shadow is meant to portray that the object is creepy or ...
0
votes
2answers
39 views

Energy conservation in Elastic collision

A question from my textbook is stated below In an elastic collision The initial kinetic energy is equal to the final kinetic energy The final kinetic energy is less than the initial ...
5
votes
1answer
90 views

Does energy conservation apply to Casimir effect?

If you cancel out some quantum field modes using two 'Casimir' plates you decrease the average energy density in the region and gain potential energy in Casimir force approximately proportional to the ...
-1
votes
1answer
64 views

Change in kinetic energy of pendulum [closed]

"An object of mass m is tied to a string of length L and a variable horizontal force is applied on it which starts from rest and pulled slowly until the string makes an angle $\theta$ with the ...
0
votes
2answers
65 views

Feynman Lectures vol.1 Chapter 4 Topic 4-2GravitationalPotentialEnergy

Could anyone explain me in simple words what is being said in topic "4-2 Gravitational potential energy" from "The Feynman Lectures on Physics, Volume I" (great book and author btw)... i don't ...
0
votes
1answer
39 views

Two black holes in rotation - Energy conservation

I was looking at this problem: Let consider two black holes of mass $M$ rotating around a point $O$ (circular montion). The first black hole center is $M_1$, the second $M_2$. Each of them has ...
-3
votes
1answer
37 views

Why is zero-point energy idolized as a good source of energy? [closed]

I've really only seen it in like liquid helium and I don't understand how it can hold the potential portrayed in the incredible movie by the main villian
1
vote
1answer
57 views

How can the momentum-position Uncertainty Principle not violate conservation of energy? [duplicate]

As far as I understand, the primary reason why an electron doesn't fall into a nucleus is that, when it gets close, it has a sufficiently high probability of having a lot of momentum to get back to ...