Energy is a quantity which gives an overview of the amount of work doable by the system.

learn more… | top users | synonyms

0
votes
2answers
38 views

Calories Burned While Hiking [closed]

I want to find out how many calories are burned on any particular hike by any particular by using a formula. I figure it's probably a simple physics question, but since I never took physics, I don't ...
2
votes
1answer
156 views

Is work is equal to $mv^2$ (without $\frac{1}{2}$)?

I was trying to come up with an equation for work that doesn't include time, because I don't know time. Here's what I did: $$ work = Fd = mad = m{v\over t}d = m{v\over\left({d\over v}\right)}d = ...
0
votes
0answers
41 views

Effects of energy loss for a damped wave

I have two questions: 1) When a lightly damped wave losses all it's energy, must it maintain it's wavelength before it dies? 2) When a travelling sine wave is damped, can the peaks be skewed from ...
1
vote
1answer
141 views

Can sound produce electricity?

Energies of wind and water can produce electricity. But, can sound energy also be used to produce electricity?
1
vote
1answer
315 views

What is the cause of the large damage by atomic bomb?

I recently read in the Feynman Lectures that when the nuclei like that of uranium which are at the crucial level of balance between strong nuclear forces and electrical repulsive forces are taped ...
3
votes
3answers
274 views

How would normal matter behave under conditions found in the core of the sun?

Considering how low the power density is at the sun's core, I seem not to be able to expect what would happen to matter in case it was thrown inside the sun's core. For example, let's assume an ...
1
vote
1answer
73 views

“Rocket in a box” thought experiment

Here's a thought experiment that I came up with a while ago. It might be hard to visualize, so I'll describe it as best I can. Take a rocket in a vacuum, in outer space. Attach a large "box" to the ...
1
vote
1answer
51 views

Why potential energy of external force on particle attached to spring is equal to full force multiplied by full displacement?

I am having quite difficult time to understand the meaning of total potential energy on spring. All references I read say that the total potential energy on particle attached to spring is: ...
5
votes
2answers
104 views

Does a reflection still transfer momentum to an mirror?

I have been recently wondering, if I take a powerful enough energy source (photon) and I have an perfect mirror exactly in front of it and assume an "emitter" shot the light towards the mirror. As ...
2
votes
1answer
73 views

What happens to the energy?

if we make a bell ring in a vacuum room for 5 mins. And then open the door, will be able to hear the sound? If no sounds vibrations are emitted to the environment what happens to the energy that ...
0
votes
1answer
37 views

Negative Energy in Inflation Theory (Low/Zero Energy Universe)

I've been reading Max Tegmark's book: Our Mathematical Universe. It's very interesting, but I wanted to know more about one particular thing. The book simplifies things and I know inflation theories ...
2
votes
2answers
117 views

Power to suspend a mass in air

How much power is needed to suspend a mass in the air? The four parts below deal with the same problem. I post them all here, should there be some subtle things I didn't see. The textbook problem A ...
0
votes
1answer
58 views

Need help in identification of formula [closed]

i would greatly appreciate it if someone could provide me with the concept to learn about this equation
2
votes
1answer
41 views

Interference and energy question here

So Im reading this material on interference and I noted the following sentence : During the interference of the light of two coherent light sources,the intensity of the radiation changes ...
0
votes
3answers
61 views

Confusion relating the application of Work-Energy theorem

Could someone kindly explain the solution to my confusion? When we walk at a constant speed up a steep hill, is work being done? Then why isn't our kinetic energy changing as work done is equal to ...
0
votes
4answers
135 views

How to measure the energy consumption class of a home appliance? [closed]

Some of you may be familiar with the EU energy consumption classes for domestic appliances (or equivalents in other areas). Let's say we have a domestic appliance which was made before the energy ...
2
votes
1answer
84 views

Making fire using a filled water bottle

I have seen videos where a fire was started using a water bottle filled with water. I guess the bottle acts like a convex lens that converges light to a focal point to start a fire. But why does water ...
3
votes
1answer
84 views

The FRW universe is NOT asymptotically flat? Its mass?

The Friedman-Robertson-Walker (FRW) metric in the comoving coordinates $(t,r,\theta,\varphi)$ which describes a homogeneous and isotropic universe is $$ ds^2\,= -dt^2+\frac{a(t)^2}{1-kr^2}\,dr^2 + ...
3
votes
3answers
91 views

Does or should the metric expansion of space imply a locally observable increase in kinetic energy?

The title is the question. Here's why it seems like local kinetic energy should increase: Numerous questions and answers here and elsewhere suggest that the reason the metric expansion of space is ...
0
votes
0answers
92 views

Is there a scientific/physics mistake in my idea?

I recently participated in the Google Science Fair and created a model/theoretical device that was capable of harvesting suns energy so much that it'd nearly increase energy produced by 3 times. But ...
1
vote
0answers
12 views

Determine the particle velocity of a pressure wave

I am using constant density wave propagators to model seismic waves in the subsurface. What I want with these acoustic waves is to estimate the energy of them at a certain grid point at a given time. ...
1
vote
1answer
46 views

What physics considerations direct the charging of cars with wireless?

Is there any frequency at which cars can be charged with using wireless? Surely, wireless transmission can be safely assumed to be a form of energy transfer, and there can be charging of cars without ...
1
vote
3answers
142 views

Energy of gravitation

EDIT: As some confusion has appeared, I want to make another clear question. If gravitational energy is meaningless in general relativity (since it is the geometry), how can one come up with the ...
0
votes
1answer
70 views

Relationship between temperature and energy

What is the definition of temperature in relation to energy? I'm mostly interested in general dimensional terms. Is temperature the kinetic energy per mass? Or kinetic energy per volume?
3
votes
3answers
237 views

Why are the energy eigenstates realized in atomic transitions?

I have a question like "Why is it often assumed that particles are found in energy eigenstates?", it is a little different, though. When one solves the hydrogen atom, one can use a polynomial Ansatz ...
3
votes
1answer
61 views

Why do safety helmets have a softer inner layer nearer the head?

I know that when an object collides onto the helmet, it causes an inelastic collision so that energy is absorbed by the structure of the helmet, so what exactly does the softer inner layer do? Does it ...
1
vote
3answers
91 views

How can gravity affect light?

I understand that a black hole bends the fabric of space time to a point that no object can escape. I understand that light travels in a straight line along spacetime unless distorted by gravity. If ...
1
vote
3answers
100 views

Is the energy of a photon continuous/discrete?

I was struggling today with this question: does a free photon have a continuous energy spectra? Free means in no context of any energy system (eg. an atom, em field). Although I'm asking myself if ...
4
votes
3answers
137 views

How do photons know they can or can't excite electrons?

This might be a stupid question, but nonetheless, it has been bothering me. If you take a photon, make it go through some atoms in a solid, liquid or whatever, then you have the chance of this photon ...
3
votes
2answers
104 views

How much work will a human do to lift a weight?

I saw a pretty simple homework question here that asked how much work it takes to lift a 200 kg weight, and while the math for a basic answer is simple the weightlifter in me instead wanted to ...
7
votes
2answers
127 views

Is there a fundamental particle that gives rise to energy?

I was wondering if there exist a particle analogous to the Higgs boson that gives rise to energy, I´m sorry it´s not the big question but I feel confused about how the universe works, also I have been ...
2
votes
1answer
175 views

Intuitive reasoning for why short wavelength photons pack more energy?

The energy equation is straight forward, yes, but is there an intuitive reason for this?
1
vote
0answers
21 views

Could symmetric molecular stretching cause a physical object to become amorphous? [closed]

I understand very little of this, but my google-foo has yielded me next to nothing, I thought I might then just ask. My real question here is if it might be possible through the use of vibration to ...
4
votes
2answers
196 views

Where do flying gas molecules get their energy from?

If you heat up water in a tank to boiling point, some of the water will turn to steam. Gas bubbles are created in the water. According to Archimedes principle, the gas bubbles will have a force equal ...
0
votes
1answer
48 views

How to work out the work done to put a satellite into orbit?

I'm having troubles doing questions that involve how to put a satellite into orbit. So we have a satellite in orbit 20500 km above earth, (and earth radius = 6380 km), the satellites mass is 1000 kg, ...
1
vote
2answers
50 views

Work and Kinetic energy rely on each other which came first?

In all the places I've looked kinetic energy is derived from the definition of work, but I don't understand how the definition of work was developed with out the concept of kinetic energy. My question ...
1
vote
1answer
33 views

Amplitude decrease during geometrical spreading of a seismic pulse

I'm looking at amplitude decrease of a seismic pulse as a result of geometrical spreading. Starting with the energy contained in a unit area, $I = E / (4 \pi r^2)$, where $E$ is the original energy ...
3
votes
2answers
1k views

Energon: is it possible?

I'm always quite curious about the "Energy cube" in Transformers, or namely Energon. Is it really possible to store energy, such as electricity, into such a compact form? safe to distribution, and ...
1
vote
1answer
26 views

Why does absorption cause seismic pulses to increase in length over distance?

The specific question I'm trying to answer is "How does the progressive loss of higher frequencies in a propagating seismic pulse lead to an increase in pulse length?" I understand how the higher ...
0
votes
1answer
62 views

Transmission/Equilibrium Question

Suppose there are two wheels linked by some kind of apparatus with a transmission, in a vacuum. Wheel A is spinning, wheel B is not. Is it empirically possible for the transmission to transfer the ...
1
vote
2answers
96 views

Bloch theorem, Energy, Free electron

I'm trying to learn on my own a bit of solid physics to tackle semiconductors afterwards. I'm struggling with the Energy versus $k$ diagrams for a free electron which shows that for a single value of ...
0
votes
1answer
104 views

Kinetic energy and potential energy variation over distance in SHM

When you compute the average potential energy of a horizontal spring mass system from the mean position to the positive amplitude A, the value comes out to be $\frac{1}{6}kA^2$. For the average ...
0
votes
0answers
56 views

Compute energy from displacement via time integration (using ODE)

How to compute energy from displacement given by solving an ODE via, e.g., ODE45. Say one has: $$ \ddot{z}+\zeta \dot{z}+z=\kappa\cos\left(\Omega t\right),\quad z=z\left(t\right) $$ and wishes to ...
0
votes
1answer
41 views

How do you calculate the power needed to keep something stationary? [duplicate]

1) If I place an object on a table, it will sit there forever. There's no change in potential or kinetic energy. If I hold the object at the end of my outstretched arm, eventually I can't do it ...
2
votes
1answer
57 views

Why is the D+T fuel inside a pellet in two distintic regions in fusion after compression

Could anyone explain why the D+T inside the pellet is in two distinct regions? And why the center is a lot less dense than the outside region? I have been trying to find answers online but i cant ...
0
votes
1answer
41 views

The formation of shockwave inside pellets in inertial confinement fusion

In the explanations i have read on the internet about ICF they all explain that the top layer of the pellet or the ablator is heated till it explodes and this produces a reaction force which compress ...
3
votes
1answer
60 views

Time Energy symmetry in General Relativity (not asking about energy conservation)

In General Relativity is there a TE symmetry similar to CPT symmetry in the Standard Model ? It's pretty easy to understand that by flipping charge and parity you merely get a time reversed equivalent ...
0
votes
0answers
43 views

Derivation of Van der Waal's Equation from Helmholtz Free Energy

From the following equation $$ f(T,v) = f_{id}(T,v) - RT \ln\bigg(1-\frac{b}{v}\bigg)-\frac{a}{v}$$ how do I derive Van der Waal's equation. In the equation above, $f$ and $f_{id}$ are the Helmholtz ...
0
votes
2answers
56 views

Faraday Effect does light bend or lose energy?

I was reading upon Faraday effect when it said Faraday effect causes a rotation of the plane of polarization That in mind, does this mean the light can be bent around or does the light loose ...
1
vote
1answer
133 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. ...