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.

learn more… | top users | synonyms (1)

0
votes
1answer
35 views

How can I interpret $P(t) = \frac{1}{Q(t)} \frac{dW(t)}{dt}$ physically?

Generally speaking, one can calculate the work, $W$ (energy) required to compress a volume, $V$ of gas by integrating the pressure-volume 'loop' in a phase-space as $$W=\oint PdV$$ where $P$ is the ...
8
votes
2answers
295 views

Internal energy of an ideal gas as a function of volume

Okay so I've been reading a bit on Thermodynamics and I found something that I couldn't wrap around my head. For an ideal gas, the change in internal energy is equal to $$\Delta U = Q + W$$ And ...
0
votes
2answers
36 views

Conservation of Energy vs Conservation of Momentum in Rotational Dynamics

It is clear to me why angular momentum is always conserved, and how in some cases energy is not necessarily conserved within the system (in those cases where bodies deform, or friction is involved). ...
-2
votes
2answers
103 views

How did physicists arrive at conclusion that the product of mass and velocity is equal to momentum?

How did physicists arrive at conclusion that the product of mass and velocity is equal to momentum? What is the intuition behind $p=mv$? I had trouble finding any sources that state the actually ...
-2
votes
1answer
48 views

work and energy dilemma in an inclined [closed]

An example problem done in my book: A driver was driving a car of mass 1000 kg through an inclined plane which makes an angle of 30° with plane with a velocity of 25 m/s . Then he saw a boy 50 m ...
0
votes
0answers
82 views

How much of this 'Slow Death of the Universe' was predicted?

In short: the energy generated in today's universe, is "about half of the produced two billion years ago" and found that "this fading occurs at all wavelengths" as yesterday news: ESO - Charting the ...
0
votes
1answer
53 views

Could light be limiting towards a more fundamental speed limit? [closed]

Could it be possible (as in strictly speaking, no evidence going against this) that light could be limiting towards a more fundamental speed, and that light truly does slow down when a mass goes a ...
1
vote
3answers
84 views

What is an EM wave? [closed]

How does an EM wave carry energy? What is an EM wave? (Is it a collection of photons?) What are the mechanics behind it? I am an engineer and I've been taught to think of light (light is my area ...
0
votes
0answers
21 views

Mass, Spin, Internal Energy and 1-Particle States in Galilean Quantum Mechanics

I have been reading an article discussing the unitary representation of Galilean group and non-relativistic quantum mechanics. The link to the article is given below. http://arxiv.org/abs/1107.2442 ...
17
votes
6answers
2k views

Will drinking ice cold water and eating cold food cause weight loss (over a period of time)? [closed]

A friend of mine has the idea that drinking cold water and eating cold food will assist them in losing weight. The core temperature of a human body is 37$^{\circ}$ C. If they drink water, at a ...
-1
votes
1answer
44 views

Reproducing electricity [closed]

We all know reproducing solar energy is possible. Same stands for mechanical energy (air, water, coals) - they are all reproducible. But what about other types of light ? A diode light for example ...
0
votes
3answers
58 views

Why can you turn on your bike without adding energy and still be moving?

There's a physical effect that I can't seem to figure out. When you are biking (on a bicycle), you have some speed. Then let's say you stop petaling and make a 90º turn to the right. You slow down, ...
-2
votes
2answers
55 views

Why is there no formula for some energies? [closed]

There is no formula for solar energy, mechanical energy etc, so Why there is no formulas for some energies?
0
votes
2answers
65 views

Energy in the Relativistic COM Frame

I have been taught that in Classical Mechanics, the total energy of a system of two particles in the Centre of Mass Frame is given by $$ E_\mathrm{total} = \frac{1}{2}MV^2 + \frac{1}{2}\mu v_r^2 $$ ...
1
vote
3answers
165 views

General relativity without energy?

I am kind of new to GR but I have been familiar with the concepts for a long time, I am getting used to the mathematics just now. My question is, what would GR predict if we would have an empty ...
1
vote
0answers
25 views

Minimal possible energy to make calculation [duplicate]

Are there any restrictions to energy that must be consumed to make calculations? Can calculations theoretically be done without consuming it?
0
votes
0answers
12 views

How much energy will fall into the eye given luminosity of display

The smart-glasses have tiny display. The manufacturer says the display has luminosity of $2000 cd/m^2$. The area of display is around $0.0002 m^2$. The reference smartphone display has luminosity of ...
0
votes
1answer
51 views

The only Energy is Kinetic Energy, isn't it? [closed]

I'm really looking for a discussion on this and don't really have a specific question. But this seems to be the best forum for such a topic. I could try to phrase this in a question, but I think that ...
1
vote
1answer
149 views

conversion of units

I have a quantity that I need to convert to different units. First, I need to note that the value is in the natural units system. The quantity is in cm^-1 (or, to be accurate, $cm^{-1}\hbar c /k$, ...
1
vote
0answers
15 views

How to solve this energy problem using trends related to impulse and momentum? [closed]

The question runs a 1kg block moves with a speed of 10 m/s. It strikes a spring that has a spring constant of 25 N/m. Determine the maximum compression of spring. The energy way of solving ...
0
votes
1answer
16 views

How is the kinetic energy of an object in collision converted to work done in deforming itself?

Usually, in a perfectly inelastic collision, maximum amount of KE is lost. I guess it depends on the rigidity of that object collision if any KE at all will be converted to work done to deform. ...
0
votes
0answers
13 views

Why does carbon help with electron transfer in a dye sensitized solar cell?

what property of carbon(soot) makes it easier for electron transfer within a dye sensitized solar cell?
0
votes
1answer
79 views

What's Wrong With This Quantum Analogy?

"Sometimes the idea of the quantum is compared to the units we use for money. A dollar can be divided into smaller units, where the cent is the smallest possible unit." A question I came ...
0
votes
1answer
38 views

Is average kinetic energy equal to the total thermal energy of a gas?

"Average KE" as in this equation: $$K_{average} = \frac{3}{2} kT$$ Since potential energy in ideal gas model is eliminated, I guess this equation is also for the total thermal energy of a gas/a ...
0
votes
1answer
84 views

Why we can't define energy in accelerating frame?

In my old unanswered question about accelerating frame, I have found (later after editing that question), that one of the keys is that energy is not defined in accelerating frame. What I do not ...
0
votes
0answers
32 views

What is the most energy efficient way to run an A/C unit?

I recently installed a 12,000 BTU Mini-Split A/C unit with an inverter - http://www.tempstar.com/products/dfac.html I was told that it uses approximately 0.6Kw/hour. What I am really curious about ...
-1
votes
2answers
47 views

The correspondence of potential energy with reality

I'm a bit in doubt about whether the concept of potential energy has any correspondence to the real world. Real world entities can't change their magnitude in an instant, nor without being affected ...
0
votes
3answers
62 views

How is Work by a System Interpretated in the First Law?

Good evening. I've happened to be sitting down today and just couldn't wrap my head around this question which seems rather simple at first. From reading about the first law and sign conventions as it ...
0
votes
1answer
74 views

Is there a formula/relationship between $q$, $m$, $c$, $\Delta T$ and $t$ (time)?

I am currently doing an experiment where I am burning methanol to test for the heat of combustion. To test this, I am heating 100g of water and raising it by 20 degrees Celsius before extinguishing ...
0
votes
2answers
27 views

How much energy is released per unit mass from depressurizing degenerate matter?

A neutron star remnant consists mostly of neutron degenerate matter. If you happened to suddenly have 1 kg of it in your lap without the pressure necessary to keep it degenerate, I suppose it would ...
2
votes
2answers
64 views

How is finite energy spread wholly in the infinite universe

We all know that energy is never lost, but it transforms into another form. Doesn't that mean that energy is not unlimited? I mean, why is it that way if it was infinite? However, if energy is spread ...
0
votes
1answer
49 views

Is Dark Energy and or Dark Matter directly proportional to EMR? [closed]

Is Dark Energy directly proportional to Electromagnetic radiation (EM radiation or EMR)?
-1
votes
2answers
35 views

seperate engines working vs single engine

What is more fuel efficient: Two identical cars running at 50mph or one being tied to the other and only the first dragging both at 50mph? Or what requires less fuel: Two cars to start from stop and ...
0
votes
0answers
14 views

What is the free energy of an ideal chain under stress?

this question is related to potential energy of a segment of an ideal chain under external force. I calculated the canonical partition function for an ideal chain ($i$ stands for a single segment ...
0
votes
2answers
76 views

Why are force, momentum, and kinetic energy derivatives of each other [closed]

Force $ma$ is the rate of change of momentum, or the derivative of momentum with respect to time $$\frac{d}{dt} mv = ma = F$$. Kinetic energy is the integral of momentum with respect to velocity: ...
1
vote
0answers
38 views

Why do particles in a medium have different speeds?

If thermal conduction occurs because of particles colliding with each other and imparting kinetic energy to each other, won’t the particles of an isolated medium collide with each other until the ...
0
votes
1answer
40 views

Producing energy with entanglement

If we entangle two electrons for example and move one of the electron to Mars for instance. Are we able to somehow transfer the kinetic force of Mars from its movement (spinning and orbitting) to ...
1
vote
3answers
76 views

A block sliding down a ramp lab (with friction), I keep getting a higher final energy than initial

A block of 55 g is sliding down a ramp of 35 degrees of inclination. The hypotenuse of the ramp is 63 cm and the height is 36 cm. vi = 0 as the block starts at rest. I did 3 trials of letting the ...
1
vote
1answer
73 views

How is energy dissipated in a travelling em wave

How is energy dissipated in a travelling em wave. Will there be any dissipation if it were to travel trough vaccum ?
0
votes
2answers
39 views

What is the work done?

A painter uses 1.93kJ of mechanical energy to pull on the rope and lift a 20kg paint barrel at constant speed to a height of 7.5m above the ground. How much work was done lifting the paint barrel? ...
1
vote
3answers
53 views

Is work-kinetic energy theorem useless?

This is how my book explains it: $W_{net} = \delta K$ Since the net work is tied to changes in kinetic energy and changes in speed, a mass must accelerate in order for net work to be nonzero. ...
2
votes
4answers
152 views

What exactly is work?

What exactly is work? My book confuses me: a force can lift an object to a height h, or it can accelerate an object through gravity. In all these cases, a force displaces an object and change the ...
4
votes
1answer
91 views

Proportionality constant in crater equations

I have searched for equations regarding craters and I came across two of them. The first one is from this NOAO website in the level two section. There, it says that, $$ D^3\propto E $$ where $E$ is ...
-2
votes
1answer
33 views

Lennard Jones Total system energy [closed]

i am trying to implement/extend an implementation of Lennard-Jones potential simulation regarding Xenon molecules (for curious ones, the code can be found here functions (force_naive->lj_force)). ...
0
votes
2answers
60 views

Electric Potential Between Two Like Charges

At the point horizontally across and equidistant from the centers of the two charges (also oriented horizontally), what is the electric potential? At that point, the electric field of the first charge ...
-3
votes
1answer
56 views

Work done by friction on a ball flying through air [closed]

A baseball of mass 145 g leaves a pitcher’s hand at 150km/hr, but due to constant air resistance, it arrives at home plate 20.0m away traveling at 145km/hr Assume that the magnitude of the ball’s ...
1
vote
1answer
31 views

Conservation of energy in a moving frame

I know a similar question has been asked but i'm still kind of stumped. Imagine the earth on the left and a small mass to it's right separated by some distance h. You are in the frame of reference ...
4
votes
1answer
35 views

Mutual capacitance upper limit

I am having trouble making an analog for mutual capacitance from mutual inductance. In circuits with magnetic coupling, there is an upper limit established on mutual inductance due to energy ...
0
votes
0answers
18 views

Fictious forces and calculation of energy + c.o.m. question

I am aware that in order for energy to be conserved the reference frame that you are using must be inertial. However, consider the situation where you are using the reference frame of the earth and ...
1
vote
1answer
15 views

Gas Cooled Fast Reactor Coolants

I know that helium and CO2 are used as fast reactor coolants, but how about other inert gasses with low neutron absorption, like argon, why do I see no papers on that? Oh and bonus question. Why is ...