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.

learn more… | top users | synonyms

-2
votes
1answer
11 views

Bounce height of ball on Mars vs Earth

I understand that if a ball is dropped on mars and on earth the ball will bounce back to basically the same height on both planets thanks to the law of conservation of energy. But can anyone prove ...
8
votes
2answers
1k views

How is dark energy consistent with conservation of mass and energy?

I initially thought that dark energy must in some way violate conservation of mass and energy since the component of the energy density of space that comes from dark energy is constant, and space is ...
-1
votes
0answers
18 views

Launching a Spring from a meter stick [on hold]

In class we are engaging in 'war games'. We receive a random spring and launch it from a meterstick at a target flat on a nearby table. we will have the variables for: ...
1
vote
1answer
44 views

Conservation of Energy in Double Slit Experiment

How is energy conserved In Young's Double Slit Experiment ? In destructive interference , energy is lost . So what happens to that lost energy ? Does it escape as heat ?
1
vote
1answer
64 views

Apparent Violation of Energy Conservation in an Electromagnetic system

As shown in the figure a beam of EMW pulse is propagating towards a nearly point charge.Here if we calculate the total energy of the system by the equation mentioned in photo - we get that the total ...
0
votes
1answer
19 views

A central force which enables a torque on a sphere - is it still conservative?

Consider the following example: Two spheres (one big, other small) standing vertically on ground. At first, the small sphere is on top of the big sphere. Then, it starts to roll w/o slipping to ...
3
votes
3answers
161 views

Is the accelerated expansion of the universe consistent with conservation of energy? [duplicate]

If energy can neither be created nor destroyed, how come the universe is expanding at an accelerating rate? Where does this energy come from?
2
votes
4answers
74 views

Is energy of a quantum mechanical moving particle conserved?

From the Schroedinger equation $$ H\psi=E\psi, $$ if we want to measure the total energy of a quantum mechanical moving particle, then we have to apply the Hamiltonian operator to the wave function ...
0
votes
1answer
49 views

Understanding the relationship between electric energy and force

I'm trying to do the following problem: One of the three types of radioactive decay is "β decay", during which protons decay into neutrons or vice­versa, emitting either electrons (β­) or positrons ...
1
vote
1answer
99 views

Violation of conservation of energy… or not? [on hold]

The work done by surface tension is double the increase in potential energy. This is a clear violation of conservation of energy. What is the flaw here? Work done by surface tension is \begin{align} ...
0
votes
3answers
507 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 ...
1
vote
2answers
52 views

Negative energy of universe

According to a little I have understood whatever we see in the universe is its postive energy and there is so an equal negative energy. Is this Negative energy the Dark energy? which is responsible ...
2
votes
1answer
124 views

Why isn't jumping against a wall an elastic collision?

According to this calculator http://www.abecedarical.com/javascript/script_collision1d.html when low mass object hits high mass object it is reflected gaining opposite velocity almost the same as ...
1
vote
3answers
106 views

Does energy conservation not hold in fission and fusion processes?

I have read that during fission and fusion processes, there is some kind of equilibrium between the single nucleus and the disintegration products, so they are constantly being converted into each ...
-3
votes
0answers
85 views

Does This Video Really Prove that Energy Conservation Can Be Violated? [closed]

I've discussed the following video elsewhere: http://youtu.be/YBMUzoUJ7ww and am more and more coming to the conclusion that the video shows for the first time scientifically sound proof that ...
4
votes
1answer
336 views

Sufficient conditions for the energy to be not conserved?

I'm almost embarrased to ask this question because I thought I was by now very confident with classical mechanics. Someone has stated that given a mechanical system with a Lagrangian $L$ s.t. ...
2
votes
3answers
391 views

Two dimensional elastic collisions with varying angle of incident

If in an elastic collision I know all initial values and that mass for each object remains constant throughout the collision (but different from one another) how can I determine their final velocity ...
0
votes
1answer
13 views

Determining a velocity value using energy conservation

The idea is to create an experiment that'll give you the initial velocity value with which you throw a ball down at 1 meter so it bounces to 2 meters. I don't have a solid Coefficient of Restitution ...
0
votes
1answer
47 views

What observations would be needed to falsify the law of conservation of energy?

I've been doing some thinking, and began to wonder: What observations have led us to the conclusion that ‘energy can neither be created nor destroyed’? Essentially, this means that the big bang ...
0
votes
1answer
63 views

How can a moving frame transmit energy (a fighter plane shoots a bullet)? [duplicate]

This question shows that a bullet shot from a flying plane receives a large amount of energy from the plane, even much more than the energy from the propellant of the bullet. But I wonder how can the ...
1
vote
3answers
3k views

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? ...
1
vote
2answers
22 views

Do transferring energy and applying force to a body imply same?

Do transferring energy and applying force to a body imply same meaning? When we say, "I throw a ball using my pushing force so on the other hand, can I say that I transferred my kinetic energy to the ...
1
vote
3answers
43 views

If a body is at rest at Earth's surface, can we say that its kinetic and potential energy are $0$ simultaneously?

If a body is at rest at Earth's surface, can we say that its kinetic energy $E_{\textrm{kin}}=0$, and its potential energy $E_{\textrm{pot}}=0$ also? Because its velocity $v$ and height above ground ...
1
vote
0answers
16 views

Energy conservation if photon absorbed below resonance

Suppose I have some quantum system (like atom) with excitation energy $E_{exc}$ which is homogeneously broadened due to finite lifetime. I shine light with narrow spectrum centred around energy ...
-4
votes
1answer
71 views

Is information a form of energy? [closed]

To better describe my question, do the following experiment: Calculate x=12+26+67+71 Now you might have spent some time in getting the answer. You burnt sugar, you used up energy to get the ...
1
vote
1answer
48 views

Determine the value of $g$ with rolling ball

At first, I thought the value of $g$ ($9.8m/s^2$) could be determined simply by placing a ball at the top of a ramp at a known height. The ball was released with no initial velocity, and the final ...
1
vote
1answer
83 views

In a CMCS 2-body system, why does the speed of the particles after collision stay the same?

A particle $m_1$ is traveling with velocity $v$ toward a stationary particle $m_2$. The velocity of the center of mass is given as $v_c=\frac{m_1}{m_1+m_2}v$. Changing to a moving coordinate system, ...
1
vote
4answers
118 views

Conservation of energy, and Newtonian physics that does not fit

Here is a theoretical example where the energy into the system does not mach the energy output. There is no friction or air resistance. A sledge with a rocket engine attached to it is lying still on ...
1
vote
2answers
46 views

Energy drain in damped oscillator

Suppose we have a mass on a spring with a damping term. The equation of motion is given by: $$m \ddot{x} = -kx - c\dot{x}$$ I believe solutions are damped oscillations of the form: $$x = x_0 ...
14
votes
3answers
2k views

Popular depictions of electromagnetic wave: is there an error?

Here are some depictions of electromagnetic wave, similar to the depictions in other places: Isn't there an error? It is logical to presume that the electric field should have maximum when ...
0
votes
1answer
40 views

Isolation of a Physical System and Energy

I'm trying to grasp basic concepts of energy and i have a little doubt regarding conservation of energy. According to Feynman book and Wikipedia, the Law of Conservation of Energy states that ...
44
votes
12answers
13k views

What happens to the energy when waves perfectly cancel each other?

What happens to the energy when waves perfectly cancel each other (destructive interference)? It appears that the energy "disappear" but the law of conservation of energy states that it can't be ...
0
votes
2answers
48 views

Conservation and forces/energy

Are there really non-conservative forces in actuality ? Feynman states in his book that in fact, all forces are conservative ( originating from conservative vector-fields ), provide we look close ...
4
votes
1answer
84 views

Is it, and if so, why, impossible to build perpetual motion machines (PMMs) in GR?

I am wondering about this. I have heard that in General Relativity (GR), the energy in a space-time may not be well-defined. If that is the case, then it would seem "conservation of energy" would not ...
2
votes
3answers
97 views

How is energy conserved in magnet?

When an object (i.e.magnetic) is attracted towards the magnet, work is done so that the energy is used but from where this energy comes from?
0
votes
1answer
43 views

Wondering about Energy [duplicate]

Me and Energy I'm trying to move along with my study of non-advanced physics but not grasping what energy really is, is driving me nuts. Whenever i see anything about energy ( Kinetic, ...
0
votes
1answer
18 views

Ballistic pendulum - are all forces conservative for this case?

For the Ballistic pendulum in the image below: Are we allowed to assume that after the bullet hit the log (mass M), then there's a conservation of energy? (Thus $\frac{1}{2}(M+m)V^2 = (M+m)gh$) ...
6
votes
3answers
279 views

Optimal speed for the water wheel

The hydroelectricity plants extract the potential energy of highly deployed massive object (water) as it falls down. Without turbine, all that energy would be converted into speed (kinetic energy) at ...
1
vote
1answer
110 views

Heat Equation with In-Depth Radiation Exact Solution

I am looking to solve the heat conduction equation in a semi-infinite solid with in-depth radiation on the domain $-\infty < x < 0$. The governing equation of this problem is: $$\rho c ...
3
votes
4answers
232 views

What is the energy of a superposition of energy eigenstates?

$\newcommand{\ket}[1]{\lvert #1 \rangle}$Suppose I have a system say SHO in a superposition of energy eigen states $\ket{n_1}$ and $\ket{n_2} $ given by $\ket{\psi} = \frac{1}{\sqrt{2}}\ket{n_1} + ...
1
vote
1answer
172 views

making an equation dimensionless

I have a balance of energy equation as following (for a spherical particle that colliding with a spherical fluid droplet) Left hand side is for before collision and RHS for after that: ...
0
votes
2answers
59 views

How is energy converted when massless spring is attached to a rigid support

Say a massless spring of length l is attached to a rigid support. It is extended to length l + x. Now at this position, the ...
0
votes
0answers
30 views

What is the connection between negative kinetic energy and tunneling?

In my QM lecture today prof showed that a particle going through a potential step for which the energy of the particle is $0 < E < V_0$ There exists a non-zero transmission coefficient into ...
4
votes
2answers
213 views

Conservation of momentum and energy in an explosion

One simple problem is physics is to determine the mechanical energy difference after an explosion. To do this, you must assume that momentum is conserved because in a explosion you have internal ...
2
votes
1answer
59 views

“Where” does dissipated enstrophy go?

We are all familiar with the kinetic energy dissipation and how it is converted into heat which can either be radiated away or go into the internal energy of the system. In the enstrophy transport ...
0
votes
3answers
51 views

Work power and energy

When you push your bicycle up on an inclined the potential energy of the bicycle and yourself increases. Where does this energy come from?
0
votes
1answer
33 views

Relationship between energy density and energy flux

I'm presently working on obtaining conservation laws via symmetries. These conservation laws are written as 2-element vectors where each element is the energy density and energy flux. To proceed in my ...
0
votes
0answers
14 views

How to conserve power at the reflection boundary of perfect conductor?

How to conserve energy during the reflection ? I am taking the abs value of $\sum E_{field}$ along spacial direction and plotting at each time step. Then it is normalized to the input E filed. ...
0
votes
1answer
93 views

Changing momentum of moving trolley

We have a trolley of mass $m$ and it is moving at a velocity $v$ along a smooth horizontal plane. It is full of water, and is leaking water at a constant rate out of the bottom of the trolley, i.e ...
1
vote
3answers
87 views

Example of law of conservation of energy

Law of conservation of energy states that "Energy of the universe remains constant. Energy can neither be created nor be destroyed, but it can be transformed from one form to another". So I ...