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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83 views

How can I set up an equation for distance traveled for a rubber band powered car?

I am to make a rubber band powered car, and I have to maximize it's distance traveled. The time taken to reach said distance, top speed of the car, acceleration of the car, is not relevant. I just ...
0
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1answer
52 views

If an electron tunnels and loses amplitude, but maintains energy; where does the rest of the amplitude go?

I'm assuming the 'amplitude' is kind of like the MeV it has on it, so could be seen as a product of the voltage applied to that electron in a field. But how can it 'lose' volts when passing the ...
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0answers
26 views

Why does kinetic energy quadruple when speed doubles? [duplicate]

Why does kinetic energy quadruple when speed doubles? Please explain (in simple terms) with examples if possible.
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1answer
91 views

Evaporate water using compressed air [closed]

I want to evaporate water by forming air bubbles which are formed by flow of compresses air through perforations. What is the energy (in KWh) input to compress 1 cubic meter volume of atmospheric ...
4
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1answer
62 views

Optimal size for a bike tire

While I was riding my bike funnily enough I wondered if there was an optimal size for a bike wheel. So I suppose that is my question, What is the optimal size for a bike wheel? If the bike accelarates ...
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2answers
88 views

A different interpretation of $E=mc^2$ but no idea what it might mean [closed]

I wanted $E=mc^2$ to look like an 'inverse square' sort of a formula. So this is what I derived: $E=mc^2$, so; $m=E/c^2$, assuming $E=E_1E_2$ (I am aware that when you decompose energy into two ...
2
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4answers
238 views

If a bell is rung in a perfect vacuum and is suspended by opposing magnets will it ever stop ringing?

As far as I am aware a bell rung in a perfect vacuum would only lose energy and stop ringing due to friction between the bell and the hanging mechanism (due to the lack of air resistance). Therefore ...
0
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1answer
64 views

Does a closed system with fixed entropy imply an isolated system?

Just first to clarify, my university notation is $$\text{change in entropy} = \text{entropy flow} + \text{internal production of entropy}$$ I am confused with the term fixed entropy. Does that mean ...
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2answers
155 views

What really happen with resonance inductive coupling

I can't figure out the picture of resonance inductive coupling I can image how magnetic inductive coupling works, It scatter magnetic around one coil and if second coil being near it then induce ...
1
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1answer
45 views

How to determine if a potential admits bound states?

According to Griffith's Quantum Mechanics, "$E$ must exceed the minimum value of $V(x)$, for every normalizable solution to the time independent Schroedinger equation" As an example, there is no ...
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2answers
87 views

can kinetic energy be independent of mass.?

Why is it said that the kinetic energy acquired by a body of after traveling a fixed distance from rest under the action of constant force is independent of mass? Nd yeah the mass of the body is ...
3
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2answers
64 views

What is precisely the energy scale of a process?

Coupling constants run with the energy scale $\mu$. But what is exactly this energy scale. My question is, if I have a physical process, how do I compute $\mu$?
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0answers
56 views

How to relate internal energy to atomic motion?

I am trying to conceptualize how atomic motion leads to the thermodynamically-defined internal energy (denoted as $U$ below) through some broad mathematical relationships. I get that the internal ...
0
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0answers
31 views

How complex is an energy balance for this problem?

Let's say I have an enclosed room in the shape of a box with forced airflow on the outer walls at an ambient temperature. Each end of the room (forward and rear) has a vent that ducts in warm air to ...
0
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0answers
38 views

What is the connection between Bragg's condition with reduced EK diagram?

In my course notes the professor mentioned that there was some relationship between the Bragg's condition and the first Bernoulli zone of the reduced EK diagram. Specifically, the boundary before ...
3
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1answer
45 views

Why is energy in a system typically able to be described using quadratic expressions?

This might be more of an applied math question. Why is the energy of a system typically able to be described using quadratic expressions. Is there an underlying mechanic that drives this?
1
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1answer
59 views

Where should five charges be placed inside a hollow sphere so as the system has the lowest potential energy? [duplicate]

I want to know the configuration where the system would be most stable.I only know basic Physics & Maths and cannot start solving the problem.I can understand it for 4 charges and 6 charges as a ...
0
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1answer
34 views

Is it possible to make use of the gluon field's energy to use is applications?

As we know most of the mass of the proton comes from the energy caused due to the interactions of the quarks with the gluon fields (reference link of this statement ...
1
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1answer
126 views

Do Waves have mass? [duplicate]

Do any form of electromagnetic waves like visible light have mass? It is known that all electromagnetic waves have energy. According to Einstein's $$ E^2=p^2c^2 + m^2c^4 $$ formula, the energy of a ...
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4answers
458 views

Is it possible to generate energy by the moon orbit?

My question could be a little bit surreal, but I was thinking about this: A hydroeletric plant transform the energy from the water passing through the turbines into electricity. Correct? If the ...
2
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1answer
90 views

Massless particle that have momentum not equal to 0

I saw some problems in special relativity that use conservation of total energy and momentum and the conclusions are spectacular. My problem is the following: how can a massless particle like neutrino ...
0
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3answers
87 views

Work-Energy conservation with friction

I didn't go to the lesson of work-energy theorem, so I miss something about this subject. I know the formulas, but I can't figure it out. This question has many quantities. Here is the problem, ...
3
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2answers
216 views

What would happen to a star if a Dyson sphere lined with mirrors reflected a significant portion of the stars light back to the star

I have looked for similar questions here on stack exchange. The closest example to this that I found is Could a Dyson sphere destroy a star. That question assumed less than perfect absorption of ...
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0answers
44 views

Particle moving under force $F=-cx^3$ [closed]

A particle with mass $m$ moves under influence of a force $F=-cx^3$, with $c$ a constant. What is the potential energy function $V(x)$? And if it starts to move from rest from position $x=-a$, what ...
1
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1answer
42 views

How do you define the total rotational energy of an object?

This problem arose when I was applying a conservation of energy argument to a mechanics problem, (a spinning coin on a table) and wasn't sure how to define the total rotational energy of the coin. At ...
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2answers
79 views

Car motor heat to drive a steam engine

Why wouldn't be able to place a car motor inside a water tank or another liquid to be heated by the motor, instead of wasting the heat and then use the steam generated, to drive a steam engine, which ...
0
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1answer
54 views

Does gravity (and all other fundamental forces, for that matter) have infinite energy as they seemingly last forever? [duplicate]

If I put a brick onto an steel platform, that platform can hold the brick A LONG TIME, if not FOREVER. Does the platform exert force? If so, then shouldn't it have infinite energy to resist the pull ...
0
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1answer
24 views

Polarized Filtering Frequency Shift?

A polarized filter is exposed to a unpolarized light source. The output of the filter should be of lower intensity, hence lower energy. Should not the filtered light be of a lower frequency to ...
0
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2answers
30 views

How does matter get the energy to repel the gravitational effects of itself to to other matter

This has always puzzled me. As i stand on the earth i require energy to exert a force over gravity to enable me to keep standing. The net force between me and the the earth is zero and thus i remain ...
0
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2answers
63 views

Calculate required power output for a laser

How to calculate power rating required for a laser in order to produce a dot at a specific distance after reflection? For example, the laser is 10cm from the mirror, at an angel of 30 degrees it ...
4
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4answers
89 views

Different kinds of energies in the form of $\frac{a_1a_2^2}{2}$

It seems to me that the energy of some kind frequently takes the form $$\frac{a_1a_2^2}{2}$$ Where $a_1$ and $a_2$ are some variables. So, for example, kinetic energy has $m$ and $v$; rotational ...
0
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4answers
167 views

Why aren't we affected by radium?

1)We have radium clocks, watches, wrist bands and many things which glow because of radium but we know that radium is radioactive so why isn't it harmfull for us when in bands, watches etc. 2)Does it ...
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3answers
47 views

When moving from one position to another at a constant velocity, how does the conservation of energy hold?

I know that this might be a duplicate question, but I have not found any satisfactory answers that clear up my lack of understanding. Here is my question. Say a sloth hangs on a tree in the middle of ...
2
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1answer
45 views

Can the Cosmic Neutrino Background be detected from a lab moving near the speed of light?

If I've understood it correctly, the energy of an object depends on the reference frame, so when you accelerate, the CMB and CNB appear to gain energy (relative to your rest frame). So if you are ...
0
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1answer
48 views

Can a solar panel work with heat?

As we know that a solar panels due to the energy of light, but can we run a solar panel with the same amount of energy provided as heat?
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2answers
38 views

What theories or formulas are involved with velocity

What theories or formulas are involved or can be added as background information in an experiment that sees a small toy car roll freely down an incline where the surface area is altered to cause more ...
2
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2answers
76 views

Lack of rigour in usual derivation of Work-Energy Theorem

The derivation of the Work-Energy theorem usually goes as follows: You define the work done on a particle under net force $\vec{F}$ as $$W=\int\limits_C \vec{F}\cdot\mathrm{d}\vec{r}$$ And then you ...
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3answers
43 views

Work and energy

when a ball of mass m is brought with uniform velocity from infinity into the g field of the earth at a distance r from it, the potential energy of the ball earth system decreases from 0 to -GMm/r. ...
0
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1answer
286 views

What factors affect the velocity of an object moving down an inclined plane?

If you have a small toy car rolling down an wooden plank, what factors would increase or decrease the velocity of said car. In the experiment my team originally stated that adding mass to the car ...
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0answers
66 views

Total Energy of Inverted Pendulum

I have to find the total energy $V$ of an inverted pendulum (rod). The following parameters and their values are given: Mass $m$ and length $l$ of the pendulum $\theta$ as the angle of the ...
0
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1answer
57 views

“Definition” of internal energy

Conversation of energy implies that if we have a thermally insulated system which goes from state 1 to state 2: $$\Delta E_{12}=E(2)-E(1)=\Delta W_{12}$$ and the 1st law of thermodynamics ...
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4answers
5k views

Why does moving through time not require energy?

Moving through the other three dimensions necessitates energy. But why doesn't moving through time necessitate energy?
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0answers
51 views

Entropy: Disorder or energy dispersal?

The first definition of entropy given by Clausius is I believe this $$S=Q/T$$ It is as I understand a common fact to understand entropy and maybe often teach it as a measure of disorder through the ...
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0answers
36 views

Experiment validating existence of virtual particle

I'm curious about virtual particle whether do they really exists, therefore I dug out an experimental theory called lamb shift by measuring the difference between the two energy levels of a hydrogen ...
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0answers
20 views

Absortion of light by a plasma

Considering a plasma generated in a fixed volume by increasing the temperature of Helium gas from the environment temperature (this temperature is not stated) and an initial presure of 0.001 Torr, to ...
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votes
8answers
3k views

Does it take more energy to open a door when applying force close to the hinge?

Assuming an ordinary hinged door (without any springs), would it take more energy to open it when applying force in the middle of the door (point b), rather than at the end of the door (point a), ...
1
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3answers
48 views

Closed-system power-generation using waterwheels

I'm not a physicist, and this question is bugging me .. :) Is it possible to create a closed power-generation system, using upper and lower water-reservoirs where a continuous flow from the upper to ...
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1answer
76 views

4-momentum of massless photons

The time component of a particle's 4-momentum is $$ E'=\frac{E-up}{\sqrt{1-u^2/c^2}}\tag{1} $$ Now suppose it is photons that you are observing from a system moving at $u$ on a line towards ...
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2answers
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Why doesn't the evening/morning sun feel much hotter on your face?

I understand that places on the Earth's surface get hotter in summer, and in the middle of the day rather than morning or evening, because the surface of the Earth is presented 'face-on' to the Sun at ...
0
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1answer
46 views

Series of parallel thermal resistance connection for this enclosure?

Let's say that I have an 2D enclosure in the shape of a pyramid with unequal areas for the faces and I am looking to determine in the inside air temperature. The parameters I know are the outer and ...