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

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2answers
465 views

What is a single word that describes the idea of the second time derivative of energy?

I think about position, its time derivative speed, and its second time derivative, acceleration. I would like to identify a single word that can be used as a handle for the second time derivative of ...
4
votes
1answer
210 views

Is there a theory which treats particles as classical point singularities?

Is there a published theory that looks at all matter as occupying no space and only being felt because of its gravitational pull? We've been taught in school that matter has mass and occupies space. ...
5
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2answers
346 views

Is the energy coming from sun to earth completely sent back?

So energy comes to earth from sun in the form of EM waves. Some of it is reflected back but some of it remains on earth and is used by plants to create food and some is used in the atmosphere creating ...
1
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2answers
372 views

Einstein's Mass-Energy Equivalence versus Quantum Kinetic Energy

Using a naive view of Einstein's Energy Mass Equivalence $E=mc^2$ (where m is mass and c is the speed of light), it seems tempting to interpret this as a quantum mechanical version of the inherent ...
1
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2answers
49 views

Energy transferring question

If I have a spring being compressed by two bodies, A and B, with different masses, how much energy would be transferred to each one when they are released and the spring expanded?
1
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1answer
108 views

Is the Energy Sharply or Fuzzily Defined in Quantum Mechanics?

According to quantum mechanics, energy of a state is uncertain within a small range in hydrogen atom. But we also know that energy of a state is quantized which is contradictory to the first. Which ...
2
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1answer
307 views

What happens to a rotating rod that breaks in two?

I know that the approximation for the moment of inertia of an infinitely thin rod of mass $m$ and length $L$ spinning around an axis perpendicular to its own axis at its center is $\frac{mL^2}{3}$: ...
3
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1answer
254 views

What “I” should use in Rotational Energy formula $(I \omega^2)/2$

$\text{Rotational Energy} = \frac{1}{2} I \omega^2$. What $I$ should be used? $I$ as a inertia tensor matrix = stepRotation * inverse moment of inertia * inverse stepRotation; Or I as moment of ...
5
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2answers
846 views

Energy operator

Does the Hamiltonian always translate to the energy of a system? What about in QM? So by the Schrodinger equation, is it true then that $i\hbar{\partial\over\partial t}|\psi\rangle=H|\psi\rangle$ ...
0
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0answers
140 views

2 streams going into an engine and 2 come out. Find the enthalpy?

Problem: Steam supply to an engine is made of two streams that mix before entering the engine. Stream 1 flows at a $.01\frac{kg}{s}$ with an enthalpy of $2952\frac{kJ}{kg}$ and a velocity of ...
3
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0answers
578 views

How do I determine the Internal Energy of ammonia at a pressure in temperature when the steam table doesn't say it

I just bought a steam table for my thermodynamics class since they don't allow use to use the one from the book for the tests. This one is different from the one in my textbook as it doesn't give the ...
4
votes
1answer
511 views

Is there something like the Poynting vector for hydraulic circuits?

The Poynting vector is a representation of the energy flux in electromagnetics, showing the amount and direction of power flow at different points in space. In electric circuits, the energy is not ...
1
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2answers
115 views

Is stopping something work?

If somebody pushes against a mass moving with $3 \frac{m}{s}$ to slow it down to $2 \frac{m}{s}$, he will drain the moving system of kinetic energy. Does he do work then or does he consume work? My ...
2
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0answers
610 views

Bungee jump physics

Question: A bungee jumper jumps from a bridge. The length of the loose rope is 30 m. When the jumper reach the lowest point possible, the rope stretches 10 m. What is the final stretch of the rope, ...
1
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3answers
723 views

Energy non-conservation for time-dependent potentials

Written in a book I read that the "total energy is not preserved when the potential depends explicitly on time", i.e. $U=U(x,t)$. Is there any proof or explanation for this?
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1answer
98 views

Mathematical Modelling for Efficiency of PV thermal technology

As the efficiency of PV thermal or wind energy decreases with time(from the installment). Is there any mathematical model that gives its relation with time. i.e., whether it is a linear decrease or ...
1
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1answer
1k views

How does liquid convert to gas on getting thermal heat energy?

Say for example, when we heat, water converts to steam gas. How does it happen? What happens underneath giving rise to breaking of bond between molecules in liquid state and spreading them in gas ...
2
votes
2answers
363 views

why egg cooks slowly in mountains?

A quick Google tells me "Because water boils at a lower temperature at high altitudes". But I am not being able to understand this answer and fill-in the gap. Like, how does an egg cook in the first ...
1
vote
1answer
204 views

Depalma Free Energy fields

Few years ago I read some papers about Free Energy, written by Bruce de Palma, a physicist who is said to be the inventor of the N-Machine, which is an device that works with free energy latent in the ...
3
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2answers
452 views

Kinetic energy puzzle

System S1 moves at constant speed V with respect to S0 in one dimension: ...
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2answers
1k views

If electric charges accelerate towards lower potential energies, why do opposite charges attract?

I know my logic must be wrong but I can't figure out why. I know that charges must accelerate towards lower potential energies simply because that's a general rule of nature. However, when you release ...
4
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1answer
161 views

Is there a theortical limit to the amount of sound-energy air can contain?

is there a theoretical limit to the amount of sound energy air can contain? In case, there is a limit, what is that limit?
3
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3answers
276 views

Do we have control on what an electron transition emits: light or heat?

I don't know quantum mechanical model. So, I'm referring to just bohr's model of atom. Any atom emits energy when it makes transition from higher excited state to lower excited state. Now, some times ...
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0answers
83 views

When will the moon fall down? [duplicate]

Possible Duplicate: Are tidal power plants slowing down Earth's rotation? I've heard that there are turbines converting energy from tidal waves. Tidal waves are created by the moon's ...
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3answers
373 views

Is the continuous transformation of energy from one form to another one free? Or it consumes some quantity of who knows what?

Sorry for the unclarity. I probably created some bias in your mind having tagged my question with energy-conservation and conservation-laws. I simply consider that, relatively independently of ...
3
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4answers
914 views

Basic question concerning pure energy

Inside the core of a star thermonuclear fusion reaction fuses hydrogen atom into helium releasing massive heat/light and energy.When a blackhole eats up enough stars and gases it devours itself by ...
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3answers
2k views

Conservation of energy and Doppler effect?

From what I understand, the frequency of light coming from the source moving towards an observer increases. From $ E=hv $ , this implies increase in energy of photon. What really is confusing, is ...
6
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2answers
384 views

What is changing in latest light bulb technologies?

I'm confused with the latest home lightning bulbs. Understanding filament bulbs was easy. For example take 220V, 100W filament bulb: Power = $V^2/R$ Filament gets heated and emits energy in the form ...
1
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1answer
580 views

How to teach the concepts of “Electric Potential” & “Potential Energy” to 10th grade students

I've got to teach the concepts of "Electric Potential" & "Potential Energy" to 10th grade students. I don't understand how to express these things and make them understand. “If you can't ...
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0answers
94 views

Masses of all the particles in the Standard Theory [duplicate]

Possible Duplicate: If photons have no mass, how can they have momentum? I'm sure this question has been asked here before but I wasn't able to find it clearly answered in one q/a session. ...
5
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2answers
1k views

Does space have to be filled with charged particles to carry electromagnetic waves?

I'm a newbie here so have mercy. I'm studying electromagnetic waves. This is the propagation of energy via the vibration of charged particles, as I understand it. A charged particle could be like ...
1
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1answer
163 views

The energy carried from one winding of a transformer to another, in quantum terms

I have read in wikipedia this statement "The energy carried from one winding of a transformer to another, in quantum terms is carried by virtual photons, not real photons" (wikipedia src: virtual ...
2
votes
1answer
135 views

potential energy of an object due to other two objects

consider object A with mass $m_{A}$ and positional vector $\overrightarrow{r_{A}}$ object B with mass $m_{B}$ and positional vector $\overrightarrow{r_{B}}$ object C with mass $m_{C}$ and positional ...
4
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5answers
7k views

How does ATP transfer energy to a reaction?

This is a question for which I've found it surprisingly hard to find a good answer. Biology texts talk mystically about the ATP->ADP reaction providing energy to power other reactions. I'd like to ...
0
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1answer
284 views

calculating of g force in fun ride

we vistited yesterday a fun park and saw a ride which was a big centrifuge only in vertical. this one had a speed meter but it was broken and i also wanted to know how much g-force is on there... so ...
6
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2answers
782 views

What is the highest energy position for a double pendulum? And for which energy positions is it chaotic?

Math/physics teachers love to break out the double pendulum as an example of chaotic motion that is very sensitive to initial conditions. I have some questions about specific properties: For a ...
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2answers
1k views

how does human brain compare to a modern CPU in energy per bit?

Can someone compare the energy efficiency of human brain as a computer ? What is the energy in joules / flop ? may be some reasonable assumptions on the computational load of common tasks such as ...
9
votes
4answers
663 views

fraction of magnetic energy stored outside a solenoid

If I have a long solenoid, e.g. length $l$ and radius $r$ with $l = kr$, where k >> 1, with a nonpermeable (e.g. air) core, how much of the magnetic energy is stored outside as compared to inside? If ...
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2answers
3k views

Finding the max height of a ball launched as a projectile using work-energy

A ball is launched as a projectile with initial speed $v$ at an angle $\theta$ above the horizontal. Using conservation of energy, find the maximum height $h_\text{max}$ of the ball's flight. Express ...
12
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3answers
5k views

When is the Hamiltonian of a system not equal to its total energy?

I thought the Hamiltonian was always equal to the total energy of a system but have read that this isn't always true. Is there an example of this and does the Hamiltonian have a physical ...
3
votes
1answer
538 views

Why is E85 less efficient than straight gasoline?

Why is straight gasoline (or whetever the mixture was before the introduction of ethanol) more efficient (ie, more miles/gallon) than E85? I've known since it's introduction that E85 was less ...
2
votes
1answer
405 views

whats the rate of energy increase required for constant acceleration between 0.0c and 0.99c?

I was wondering how much energy would be required to accelerate 1000kg to 0.99c at 1G. What I don't understand is what the rate of increase of energy is required as velocity increases. I was looking ...
2
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6answers
1k views

What's the problem with solar energy?

What "breakthrough" from a theoretical point of view is needed for solar energy to become feasible energy alternative?
5
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1answer
364 views

What type of solar energy technology has the most future potential?

In terms of dollars per watt, using theoretical efficiency limits, what technology holds the most promise to become the primary solar energy capture technology? My hunch is carbon-based modules, ...
2
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2answers
630 views

Limit on geothermal energy that could be extracted before the earth's magnetic field collapsed?

This is more of a theoretical thought-experiment question. Basically, how much geothermal energy can we extract before the loss of the magnetic field makes it a terribly bad idea? Will the ...
0
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1answer
115 views

People eating and gaining energy

Let's say we have 100 grams of chocolate which has 571 kilocalories (so it's about 2.4 megajoules) and we have barbell which weights 100 kilograms and need to lift it to 0.5 meters height. So how ...
1
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1answer
274 views

Energy storage and battery banks [closed]

Why is it not possible to store windfarm energy in battery banks? A lot of energy isn't being used when wind farms are at peak and we have no way of storing it. This is wasteful. So why don't we use ...
2
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1answer
2k views

Fuel usage at the same constant rpm at different gears

I've had a discussion with my father today, about the fuel usage of a vehicle at the same rpm, but a different gear. He claims that the following situations have the same fuel usage: ...
2
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2answers
2k views

In summer are the upper storey flats more hot or the lower storey flats?

I have often heard neighbours talking things like in a multi storied apartment, the upper flats are more hot in summer then lower flats (or vice versa?) and similarly for some comparison in winter? ...
2
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1answer
3k views

calculating thermal energy [exam prep]

I'm preparing for a grade 11 physics exam but having trouble with a question: a 19.9kg mass slides in a straight 28.8m line experiencing friction with a coefficient of 0.105, how much thermal energy ...