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

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Solar plants and energy conservation

I'd like to apologise if this question is stupid or if it was asked ten thousand times - I haven't found an answer to it. Quite possibly due to mediocre English or abominable knowledge of physics. ...
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812 views

Where do planets get energy to revolve around sun? [duplicate]

We know that every planet in our solar system revolve's around the sun in a particular orbit. But were to they get the energy to revolve around the sun. And why do they not drop into the sun there is ...
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Perspective and changes in kinetic energy

Say you have two planes flying next to each other at the same speed and one decides to pick up speed by burning a tank of rocket fuel. If someone on the ground wanted to know that plane's new speed ...
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39 views

Necessity of the Notion of Work and Kinetic Energy

I've worked through many example problems in my college physics text in the section on kinetic energy and work. I noticed that if the desired quantity is velocity or force, they can be solved entirely ...
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Does $E = mc^2$ apply to photons?

Photons are massless, but if $m = 0$ and $E=mc^2$, then $E = 0c^2 = 0$. This would say that photons have no energy, which is not true. However, given the formula $E = ℎf$, a photon does have energy ...
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59 views

permanent magnet energy field [duplicate]

Please explain to me this: What is the physical mechanism of the field and atraction force; in which way a force (electro, magnetic or gravity) is transmited between two objects? I will try to ...
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138 views

How to calculate the amout of time for oil to get out from a pneumatic cylinder?

I have a system. You can assume it is just a 1" diameter steel pneumatic cylinder (1 foot long). Assume we ignore the bore size issue at this point. One chamber is filled up by oil (6" of volume), ...
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1k views

Why does a gold leaf appear blue if made very thin?

Is this to do with excitation of electrons and emission of photons? Or is it more to do with the structure of the gold I.e. Only small wavelengths being able to pass through gaps between atoms? EDIT: ...
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Does ABS shorten stopping distance of a car?

ABS, from German Antiblockiersystem, is a device put in almost every new automobile. The web has lots of explanations about the system, how it works, but I don't understand how it shortens the way of ...
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40 views

If kinetic energy is equal to force x distance, does that mean a mass traveling in the vaccum of space keeps getting kenetic energy

This is something I don't understand about it because if the speed remains constant, nothing changes about the objects energy.
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64 views

Are sound waves adiabatic or isothermal?

I am doing a presentation on sound waves and I need to know if they are adiabatic or isothermal. I know that they can generate heat, but is the amount of heat created so small that it can still be ...
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68 views

Is the work-energy theorem valid for only particles or rigid bodies as well?

Is the work-energy theorem valid for only particles or rigid bodies as well? Most places where I have read this seem to claim the latter. But an example I thought up has been troubling me. Consider ...
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How can I explicit the energy dependence of the Maxwell-Boltzmann distribution?

I'm having a bit of a problem figuring out the energy dependent Maxwell-Boltzmann distribution. According to my book (Ashcroft & Mermin) they write the velocity dependent distribution as: ...
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219 views

Why aren't the energies of two systems in thermal equilibrium fixed?

In the derivation of the Boltzmann distribution they consider a system $A$, enclosed by a diathermal wall in a heat reservoir $R$. Then they calculate the probability that the system $A$ is in an ...
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235 views

Is force the derivative of energy?

In my lecture today my professor briefly mentioned that force is the derivative of energy but I did not really get what he meant by that. I tried to express it mathematically: ...
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7answers
2k views

How was the formula for kinetic energy found, and who found it?

My questions mostly concern the history of physics. Who found the formula for kinetic energy $E_k =\frac{1}{2}mv^{2}$ and how was this formula actually discovered? I've recently watched Leonard ...
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1answer
25 views

Kinetic energy for rotating round body having its COM not at the centre

Say I have a round object, whose center of mass is NOT in its center. This can be caused due to a hole or non uniform distribution of density. The object rolls on the ground with velocity of ...
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1answer
43 views

Where does energy goes when I work out?

Let's say I am using a machine to lift weight by pulling a bar. When I do that, the state of the machine is exactly the same at the beginning and the end of the workout; no heat has been generated ...
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448 views

Has $E=mc^2$ been experimentally verified for macroscopic objects with potential energy?

In relation to this question: What is potential energy truly?, I'm wondering if $E=mc^2$ has been experimentally verified to hold true for macroscopic objects with increased potential energy? I'm ...
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126 views

What happens to kinetic energy of an object when i stop its motion? [duplicate]

Assume an object is moving and it is stopped at a point . Now kinetic energy will transform into some other energy . what can be those energies and on which cases these will happen respectively ? ...
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Do virtual photons have a frequency?

Real photons do have frequencies, which is directly related to its energy. So, can virtual photons that take part in EM interactions have frequencies too? When my hand is pressed up against a glass ...
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How to compute minimum shallowness of quantum well to have at least one bound state?

Given a potential $V$, how does one compute how shallow the potential can be such that it allows at least one bound state?
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1answer
25 views

time factor of heat increase (specific heat)

It takes 4 joules to bring 1 gram of water up 1 degree, but for how much time - 1 second? If not, how much and how to calculate it?
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1answer
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Relativistic kinetic energy versus classic kinetic energy [closed]

I have a homework problem where I am getting the wrong answer and I just want advice on the route I took. So I am told that electrons in a television set are accelerated through a potential ...
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120 views

Can diffusion produce energy?

A friend and I recently got into a silly argument where I stated pure diffusion can't produce energy since diffusion are a part of passive transport. He stated if we If we have tinny ...
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54 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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1answer
17 views

Pump sizing for slurry removal

on our farm we need to pump slurry from an underground tank up into an open air temporary slurry holder. I understand that to calculate the power required to pump the slurry up out of the tank is ...
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66 views

If a propane torch is rated at 200,000 BTUs, what does this translate to in terms of joules/second?

If a propane torch is rated at 200,000 BTUs, what does this translate to in terms of joules/second? Not exactly a physics question per say, but it falls in the realm. How do I convert/understand ...
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How efficient is an electric heater?

How efficient is an electric heater? My guess: greater than 95%. Possibly even 99%. I say this because most energy is converted into heat; some is converted into light and kinetic energy, and ...
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Why do almost all nuclear reactions release energy?

I'm just wondering why almost all nuclear reactions release energy, in a typical way, the mass defect is transformed into energy ? Is there a nuclear reaction that gains mass (resp. energy)? or most ...
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Are there any theoretical limits on the energy of a photon?

Is there any lower or upper limits on the energy of a photon? i.e. does the mathematical framework we currently use for Quantum Mechanics blow up when a photon surpasses a certain upper limit of ...
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91 views

Is energy affected by forces?

Curious, is any certain form of energy, such as heat, affected by a force? Can you push energy from one place to another?
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782 views

Why does Energy-Momentum have a special case?

I was reading Energy-momentum, and I came across this simplified equation: $$E^2 = (mc^2)^2 + (pc)^2$$ where $m$ is the mass and $p$ is momentum of the object. That said, the equation is pretty ...
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1answer
51 views

Increasing the efficiency of photovoltaic power cells

Given that solar cells use one or more semiconductor materials to convert light to electricity, and that the efficiency of that conversion is dependent on the material and the wavelength of the light, ...
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784 views

Why isn't perpetual motion possible, even though we are so technologically advanced?

Why perpetual motion wouldn't be possible if we are so technological advanced? It is just a thing that I was wondering for too long. I mean, we are able to create so powerful permanent magnets, like ...
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In special relativity what is the energy of a macroscopic body?

Is the energy of a macroscopic body in special relativity still given by: $E=\gamma m c^2$? If so why do we not need to consider the motion of the individual particles that make it up? Is this because ...
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52 views

Is it possible to calculate the energy of a spark?

I am not a physicist, but this question came to me and I need to answer it, and I think that you guys can help me. Actually my question is just like in the title. Is it possible to calculate the ...
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What are high energy photons?

I have often read the term High Energy photons, does this mean that there do exist photons with low energy? Aren't they supposed to have constant energy according to $E= h\nu$?
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Where does the energy required to stop a moving body come from and go?

For a long time, I have been thinking about this: In order to stop a moving body, I have to apply impulse to change the existing momentum to $0$. For the impulse I have to impart force on the moving ...
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Does a reflecting object move faster than one that does not reflect?

Suppose you have two objects with the same mass and shape, such as a ball, and the only difference between the two is that one reflects light and the other does not. Would one object's velocity be ...
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1answer
72 views

Elementary questions about where energy is stored in solids

I have the following question, I have no relation to the study of Physics in any way, but the question has been teasing me for some time. Please accept my poor physical terminology. Here we go... ...
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Do we really not know why atoms 'decide' to produce a photon?

I was watching the Cosmos documentary where Neil deGrasse Tyson explained how certain energy photons get absorbed by an atom, which causes the electrons of that atom to climb into a higher energy ...
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Flatness and Kinetic Energy

Why the curvature parameter can be interpreted as the difference between the average potential energy and the average kinetic energy of a region of space? Curvature ...
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Negative temperature thermodynamics

I asked this question about thermodynamics. I considered $$T=\frac{\partial U}{\partial S}$$ at constant $V$ and $N$ (number of particles), but now I can't figure out the change of $U$ with respect ...
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1answer
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Lagrangian under time transformation

Given a Lagrangian $$L(q,\dot{q},t)=\sum_{ij}a_{ij}(q)\dot{q}_i\dot{q}_j-V(q_1,q_2,\cdots,q_f)$$show that under a time transformation $t=\lambda T$ ($\lambda$ = constant), the invariance of ...
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How are the CPU power and temperature caculated/estimated?

From Wikipedia The power consumed by a CPU, is approximately proportional to CPU frequency, and to the square of the CPU voltage: $$ P = C V^2 f $$ (where C is capacitance, f is ...
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118 views

Is conservation of energy a set of principles that is inevitable in any 'possible world'? [duplicate]

It is usually stated in various books or stories 'Energy can't be created or destroyed , but is conserved'. I guess this is within a closed system. Are there any axioms or principles in physics that ...
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Gravity and its energy

Where does gravity get its energy from? So, I'm taking a high school environmental science class and we just started a unit on energy. We were talking about different types of energy and one was ...
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How can I determine density of a gas only given temperature?

I have a homework problem where exhaust is traveling through an exhaust system (assumed to be air for simplicity) from and engine and then released into the atmosphere. The exhaust is at a temperature ...
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Is it true that a processor with a higher temperature uses inevitably more power in comparison with a processor with a lower temperature?

If a processor has a higher temperature, can you be sure it it consumes more power than a processor with a lower temperature? And is the reverse relationship true? A processorchip with a higher mean ...