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

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Does a pulled rubber band contain as much energy as a twisted rubber band?

lets say I take two similar rubber bands. One of them I pull until it almost reaches its breaking point. The other I twist until it almost reached its breaking point. Do both of these rubber bands ...
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26 views

Perpetual Mobile and Gravitation

I have fundamental question about what is called the “law of conservation of energy”. We all hear about the tidal power stations which using the tidal power. The source of the tidal power came from ...
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19 views

Ratchet gear efficiency? [on hold]

Some gears can reach 98 - 99% energy efficiency in power transmission Does anyone know ratchet (one direction gear) efficiency?
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21 views

What is the fluctuations of the energy of a simple harmonic oscillator? [on hold]

$$\begin{align} \varepsilon&=\frac{\vec{p}^{\,2}}{2m}+\frac{K}{m}\vec{q}^{\,2}\\ \rho(q,p)&=\biggl(\frac{\omega}{2\pi k_BT}\biggr)^3e^{-\frac{\varepsilon}{k_bT}} \end{align}$$ where ...
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41 views

can one measure energy to a finite accuracy?

Can one measure energy to a finite accuracy in bounded amount of time? I don't know much about QM, but someone told me that the energy-time uncertainty principle says that it would take infinite ...
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2answers
81 views

How to combat the black-body temperature of an object?

I'm trying to model the temperature of a large spacecraft for a space colony simulation game I'm working on. In another question, I checked my calculations for the steady-state black-body temperature ...
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1answer
31 views

Maximum length stretch of vertical spring with a mass? [on hold]

Having a vertical spring, if we hang a mass to it, what is the maximum stretch length of spring? and how big should be mass to break the spring?
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1answer
29 views

What's wrong with this temperature-in-space calculation?

I'm trying to calculate the steady-state temperature of a body in space, but my numbers are coming up much too small. For example, for a 1-meter cube, I'm getting a temperature of 194 K (or -81 C). ...
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60 views

How is Energy Distributed within a Electromagnetic Wave?

Let $$\hat{H}$$ Denote the full energy of the electromagnetic wave. Now is it right to assume that $$\hat{H}=\sqrt{2\hat{H}_y^2+\hat{H}_x^2}=\sqrt{2\hat{H}_z^2+\hat{H}_x^2}$$ If not, what is ...
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276 views

What exactly does the Hamiltonian operator tell us?

I'm confused about how energy and time are linked. On the one hand, the Hamiltonian seems to describe the time evolution of the system because in the time dependent Schrodinger equation, $$ \hat H ...
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2answers
494 views

Is there a relationship between the energy of a photon and the energy of an electromagnetic wave?

If the energy of a photon $E_{p}=hv$ And the energy of an electromagnetic wave is $E_{w}\propto \hat{\mathbf B}^2$ What is the relationship between $E_{w}$ and $E_{p}$?
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Bound states, scattering states and infinite potentials

I am doing my first semester of Quantum Mechanics and we're using Griffith's Introduction to Quantum Mechanics. As he is introducing the Dirac delta function potential he explains bound and scattering ...
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Is energy since the big-bang still here in the present?

Based on the concept that energy can never be destroyed and is only transferred. Does it mean that energy since the formation of literally everything still here today?
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58 views

energy required to start and then stop rotating an object, when we have gravity

Imagine an arbitrary object with center of mass at the red dot in the picture, rotational inertia from the point of the hanging: I, hanging from a fixed point, what is the energy required to start ...
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2answers
71 views

Why do 2.4GHz frequencies offer greater range than 5GHz routers?

I would've thought that as 5GHz is a higher frequency, and it carries more energy, it would be able to pass through walls much more easily compared to a 2.4GHz frequency- similar to how short ...
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17 views

What is the total observational energy of the universe? [duplicate]

Based on what is measurable, how much energy is in the universe if the initial time is the big bang and the final time is the present?
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2answers
49 views

What is the change in energy of $ \Delta e = h \nu $ in respect to?

I saw this equation today when calculating energies of photons of different frequencies, and noticed that the change in energy is a product of plank's constant and frequency. $$\Delta e = h * \nu $$ ...
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1answer
25 views

Spring launches a mass on an incline plane with friction, find the height [closed]

So I've calculated the answer to this problem, but my answer is different from my book's, so I'm trying to find the error. A spring with coefficient $k=600N/m$ launches a mass of $1.2kg$ from an ...
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2answers
38 views

What is the percentage of energy recovery in Kinetic Energy Recovery Systems(KERS) in cars?

Kinetic Energy Recovery Systems (KERS) use flywheels to recover energy from the kinetic motion of cars. They use a rotating flywheel that generates energy as it rotates- this generates the electric ...
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45 views

How much energy is needed to heat your body in water? [closed]

How can we calculate (or approximate) the energy (in kJ) needed by our body to keep it constant at $36.6^{\circ}C$ in a swimming pool at $\sim 28^{\circ}C$ for 30 minutes? Body is naked and fully ...
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62 views

Definite energy states for a single non-relativistic particle with a time dependent potential

Do definite energy states exist for a single particle when its potential itself changes with time? I tried solving it and the equations seem to show that they do not exist. But then i am confused as ...
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1answer
35 views

About how much force would something have to exert to be effectively unstoppable? [closed]

Assuming an object is moving in a straight line propelled by a force. How much energy would that force have to exert so that there are no known forces or objects that could stop it from moving in that ...
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829 views

What really happens atomically in an explosion? [migrated]

Let's say a room is filled with butane, I then throw a cigarette into the room. What happens to the atoms/molecules of the butane when they are in contact with the heat from the cigarette?
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How to calculate the heat transfer rate between the liquid and the gas?

Let water (liquid) be in a chamber (with no heat transfer to the walls). The gas is the residual space above the liquid, meaning that the contact surface is the surface of the water. Given the gas ...
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49 views

Space curvature based on net energy = 0

In Neil DeGrass Tyson's epic video, at 2:26:50 ...
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30 views

Alignment of a system in equilibrium and its potential energy

Consider a flexible free conductor which is placed near a strong long bar magnet. How will the the conductor arrange itself if current is passed through it? I asked my professor: he gave me a hint ...
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36 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 ...
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1answer
154 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 = ...
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34 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 ...
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133 views

Can sound produce electricity?

Energies of wind and water can produce electricity. But, can sound energy also be used to produce electricity?
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310 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 ...
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264 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 ...
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1answer
58 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 ...
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38 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: ...
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96 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 ...
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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 ...
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1answer
29 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 ...
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112 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 ...
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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
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1answer
40 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 ...
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59 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 ...
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4answers
132 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 ...
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1answer
80 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 ...
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1answer
81 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 + ...
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3answers
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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 ...
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87 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 ...
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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. ...
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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 ...
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136 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 ...
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1answer
68 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?