Energy is the conserved quantity associated to time-translation invariance and represents the work a system is capable of doing. Use this tag for questions about energy, and consider adding [tag:energy-conservation] if it is specifically about its conservation.

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Relation between Newtons and Kilograms

Work is expressed as W=F*d, where the F is in Newton, d is in meters and result ...
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Which particle rolls faster? Is the speed of the particles which are rolling differs with their shape?

A solid disk and a solid sphere each of them has the same mass and same kinetic energies, which one is faster?
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645 views

How we can find the kinetic energy? [closed]

A solid disk of mass m is rolling along a surface its center has velocity v what is the kinetic energy of disk?I cannot solve the problem,
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Are there devices which convert thermal energy to electric energy?

Converting optical energy to electric energy is a huge business based on the photovoltaic effect. Is there an analogous effect for phonons? Are ther devices which convert phonon energy to electric ...
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657 views

Error Analysis, Change in momentum, Kinetic Energy

If momentum of an object is increased by 10%,then its kinetic energy will be increased by? Well, I don't need the solution logically by calculating the change in Kinetic Energy etc, but my question ...
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Painting wine botles [closed]

Yes, it's a physics related question. Read on. I know from general knowledge that in order to produce a decent wine, you must keep it in a dark place. Therefore, from my knowledge of physics I guess ...
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Why do we need the quantity momentum?

Why do we need the quantity Momentum in physics when we have the quantities like Force and Energy? Isn't it possible to substitute the usage of Momentum with equivalent of Force and Energy?
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How do laser rangefinders work when the object surface is not perpendicular to the laser beam?

I find the functioning of a laser rangefinder confusing. The explanation usually goes like this: "you shine a laser beam onto the object, the laser beam gets reflected and gets back to the device and ...
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2answers
104 views

Is there any correlation between the energy density fluctuations of two separate systems in a vacuum state?

I think the title says it all. What I am curious to find out is if there are any observable changes in the fluctuations of zero-point energy in a vacuum state system that are the consequence of ...
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1answer
288 views

Man on treadmill and energy/mass conservation

Suppose we put a very obese man inside a large air tight isolated room with a treadmill and he runs on the treadmill for 24 hours and at the end of the day he sees his weight has come down (mostly ...
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2answers
322 views

Are the higher-order terms in the series for energy really negligible?

To show that energy in special relativity reduces to $E=m+mv^2/2$ for low velocities, if we make a Taylor expansion of $m\gamma$ around $v=0$ we get $$E=m+mv^2/2+3mv^4/8+\cdots$$ But why can we cutoff ...
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Energy efficiency of antimatter producion [duplicate]

Possible Duplicate: Matter - Antimatter Reactory Practicality Certain reactions in particle accelerators lead to production of antimatter, which can then be collected in noticeable ...
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1answer
605 views

Wind Turbine Impact

OK, I'm not sure this is not a silly question, but here goes. I've often wondered what the impact is of wind turbines on the weather. My question is, since wind turbines transform wind energy into ...
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How do we perceive hotness or coldness of an object?

Some objects, especially metallic ones, feel cold on touching and others like wood, etc. feel warm on touching. Both are exposed to same environment and are in their stable state, so some kind of ...
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1answer
236 views

Hamiltonians and Lagrangians, Euclidean and Hyperbolic: Are they related?

The Lagrangian of a system is the difference between its kinetic energy $T$ and potential energy $V$, and is relativistically invariant: $L = T - V$ The Hamiltonian of the same system is the sum ...
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1answer
375 views

Historical and philosophical reflexions about the concept of energy? [closed]

Perhaps you know the books: Concepts of Mass in Contemporary Physics and Philosophy Concepts of Force: A Study in the Foundations of Dynamics by Max Jammer, which discusses mass and force from a ...
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316 views

Slackline Jump Tension

So a slackline is basically a bouncy tight rope. I found a site that has a calculator for the tension of a static slackline ...
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2answers
246 views

Is it possible that windmills can consume the wind?

Can windmills allow us to consume (and, eventually, over-consume) the wind as a natural resource somewhat in the same manner that we are over-consuming many other natural resources?
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1answer
77 views

is it possible to gain from charging cold battery

Is it possible to get higher load of energy into a battery if you charge it when its cold eg. +9C? the battery is emptier, but does it let the power in? Is it safe?
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Carrying water on person, or on the frame when bicycling

So, the question is as follows: What is the difference in work exerted by the rider in the two following scenarios? a) Rider + bike. Water carried in a holder on the frame b) Rider + bike. Water ...
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1answer
154 views

How is/do they plan on having fusion energy collected at the National Ignition Facility?

I was just watching a program on television showing how the method they use at the National Ignition Facility to attempt to achieve fusion is to fire extremely powerful lasers at a small pellet of ...
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2answers
180 views

Does using batteries in a series raise the overall Wh's of the batteries used? Why/Why Not?

If one has 2 batteries of 6 Volts each with 500 mAh each, then separately the batteries should provide 6 Volts * 500 mAh = 3 Wh each or 6 Wh total. However would it be the case that if someone where ...
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1answer
243 views

Decay of particle (for example $\pi^+$); Find energy [closed]

I don't understand how to solve this: A $\pi^+$ decays into a muon and neutrino. Find the pion's energy if max $E_\nu$ / min $E_\nu$ = 100/1; $m_\nu = 0$ $m_\pi*c^2 = 140\text{ peta-eV}$
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1answer
186 views

Is energy “destroyed” when walking?

Conservation of energy states energy can't be destroyed, but isn't energy used up when walking in a straight line? If your not walking up a slope, kinetic energy isn't converted to gravitational ...
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4answers
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Expected Energy Production From High Efficiency Solar Cells

First, a bit about my thoughts. I believe we have the capability today to provide energy, water, food, education, and transportation to every man woman and child on the planet. To that end, I would ...
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1answer
114 views

Is it safe for astronaut to do this “dangerous” movement?

So, if the astronaut is working outside the space station in thew space, could he not tie himself onto the space station and if he is going further away of the space station, i think he could just ...
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2answers
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What's the relationship between an object's color and it's energy?

All else held equal, which has more energy: a violet-painted teacup or a red-painted teacup? I know that violet light has more energy than red light, but does this mean that the inverse holds true ...
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Cosmic ray hazards

The Pierre Auger Observatory site mentions the detection of a 3E20 eV (48 J) cosmic ray whose energy, well above the GZK cutoff, was based on an analysis of its atmospheric shower. This was equivalent ...
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1answer
237 views

Could ions emitted by an ion thruster represent any realistic danger?

As ion thurster designs improve, the ions emitted could have a velocity (relative to the spacecraft) of well above 10^5 or even 10^6 m/s. It the likelihood of any such ions ever hitting a human ...
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1answer
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What does the Fermi Energy really signify in a Semiconductor?

In understanding the behavior of semiconductors, I'm coming across a description of the Fermi Energy here and at Wikipedia's page (Fermi Energy, Fermi Level). If I understand correctly, the Fermi ...
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61 views

Taylor approximation of e(v) [closed]

Relativistic mass $\displaystyle m(v)=\frac{m_o}{\sqrt{(1-(v/c)^2}}$ $m_o$ = mass of object measured at rest $c$ = speed of light ($3\times 10^8\;m/s$) $v$ = speed If the total relativistic energy ...
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1answer
574 views

Conservation of Energy in Special Relativity

In classical Newtonian mechanics, from what I understand, conservation of energy stems from the fact that all known forces are conservative forces, and vector calculus tells us that they can be ...
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1answer
289 views

Does friction act in the same way in different directions?

A physics textbook is launched up a rough incline with a kinetic energy of $X$ joules. When the book comes momentarily to rest near the top of the incline, it has only gained ($X-20$) joules of ...
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128 views

What are some ways that humans could have influence over what sequence a star was in?

How would a society go about either preventing our sun in its primary sequence from going into a Red Giant a billion years from now? Or perhaps, accelerating the process of going from main sequence ...
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1answer
539 views

How did the energy/entropy/volume/pressure/temperature relationship exist at the Big Bang and how did it evolve thereafter?

According to the current Big Bang with inflation cosmological model? I was under the mistaken impression that there was very low volume, very high temperature/pressure, very low entropy and the Big ...
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2answers
542 views

how does heat energy start to speed up a gas molecule?

If it was possible to place a single gas molecule in a cell and freeze it to near absolute zero. What would the molecule do as it thawed out? Would it translate the heat energy into it's electrons ...
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206 views

Simple: What do these ballistic impact numbers represent?

I bought physics for game programmers, found here, today to study ballistic impact, but I'm confused as to where a few numbers are coming from. I'm basically looking to understand what the values ...
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175 views

Matter - Antimatter Reactory Practicality

With current technology, would the energy released by a matter-antimatter annihilation be more than the energy needed to created the antimatter in the first place? Would it be worth it? Just curious, ...
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2answers
195 views

Which new insight did $E=mc^2$ give us?

I had a special relativity course at university. Now I'm trying to extract what new insight $E=mc^2$ did give us. I mean that moving mass has/is energy (kinetic) not new. The energy merely changed ...
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Proportion of energy compared to mass in universe

In Wikipedia (http://en.wikipedia.org/wiki/Dark_matter), there is a picture that shows us the proportion of matter and energy in the current universe - CMB. It seems to suggest there is nothing that ...
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239 views

Mathematical question on Collisions [closed]

A 2.5kg ball travelling with a speed of 7.5m/s makes an elastic collision with another ball of ...
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1answer
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How do kinetic energy and linear momentum relate?

It took me quite a long time to click my gears in place and even then I'm not sure it's completely correct. The problem is that I need to understand these concepts (physics concepts; not just these ...
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2answers
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Rotational kinetic energy during vertical circular motion of a particle

Why is it not necessary to take into account rotational kinetic energy when using the Law of Conservation of Mechanical Energy to solve vertical circular motion problems? After all, the particle is ...
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3answers
192 views

Lightning Power?

What is the power source of a lightning? It doesn't consume fuel, nor an atomic fission/fusion, but it discharges a large amount of energy. Is it feasible to create an artificial lightning using the ...
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929 views

Does opening or closing the window in a non-AC car in the summer affect how much heat is felt inside?

This will perhaps look like a very basic and trivial question. But I find it confusing. As an experience, when you are travelling in non-AC car in summer, have people felt if putting on or putting off ...
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220 views

Is the free energy bounded

Can we say that the free energy of a mixture of a finite number of fluids situated in a bounded container $\Omega$ is bounded? I was thinking of this as an optional hypothesis for one ...
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How does energy depend on frequency in an alternating current circuit?

In what relation is the energy input in an alternating current circuit to its frequency? I'd guess I have to compute something like $$E=\int P(\omega,t) dt=\int U(\omega,t) I(\omega,t) dt, $$ but ...
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Connection between entropy and energy

An isolated system $A$ has entropy $S_a>0$. Next, the isolation of $A$ is temporarily violated, and it has entropy reduced $$S_b ~=~ S_a - S,\space\space\space S\leq S_a.$$ Is it true to say: the ...
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How does the energy of a sound wave decrease with the distance

More precisely, how small is the potency a listener hears, compared to the potency of the emitter. I'd like to present a simple and yet reasonable approximation, to a high school audience (I am a ...
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System moves away from equilibrium $\rightarrow$ it has energy added?

Suppose there is an isolated system $A$ at time $(-\infty, t_1)$, whose entropy is $S=S_{max}$, i.e. it is at thermodynamical equilibrium. Between moments $[t_1, t_2)$ the isolation is violated and ...