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

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510 views

What is “Energy” of a vacuum in the context of quantum theory?

I'm not a physicist or cosmologist, so I hope I am asking the right question with the right words here. My question regards the word "energy" as it pertains to quantum vacuum states, and to concepts ...
2
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3answers
234 views

Where is the potential energy due to internal interactions in total energy?

In thermodynamics the total energy of a system consists of kinetic energy of motion of the system as a whole, potential energy of the system as a whole due to external force fields, and energy ...
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2answers
465 views

Why does blowing on hot coffee cool it down?

And will it cool off faster if you blow across the top of the cup or directly into the coffee? Does it have to do with the fact that when you blow across the top of the cup the velocity of the air ...
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0answers
38 views

Polarizable molecule in E-field

If we have a linear molecule with a dipole moment $\mu$ in a static electric field $E$, the potential is given by $V = - \langle \mu,E \rangle$. What is the appropriate equation for the potential if ...
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1answer
41 views

Is Red-Shift experiment correct?

I been reading: http://www.mth.uct.ac.za/omei/gr/chap5/node2.html. The website seems credible with its contact details & location being extremely accurate and easily verified, and its mathematics ...
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1answer
68 views

How do I describe the energy an electron gains (and loses) in a circuit?

I am looking at the simple circumstance of an electron traveling through a long wire by a potential. I see how one would be motivated to use the usual formula, W=F*d, to describe the electron's net ...
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3answers
274 views

Magnet motor free energy generator [duplicate]

Is it possible to run a fan without electricity? like the one show on this website? http://free-energi.com/index.php?a=2
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2answers
70 views

Changing from potential to kinetic energy

During a conversation with a friend, I began to wonder if there's is a term for the transformation of potential energy to kinetic energy, and vice versa.Is there a term for the process of converting ...
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1answer
78 views

How to calculate energy to start movement?

So let me try to explain a little bit. Lets say I have a robot on wheels. I want this robot to push a block. Lets say the force to produce in order to move that block is 100N. How much energy will I ...
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1answer
136 views

Conservation of energy and momentum via the continuity equation in asymmetric time and space translation

I am confused about energy and momentum conservation, time and space translation symmetry, and the continuity equation. Suppose we have a mass $m$ in inertial space far from any gravitational ...
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2answers
60 views

Turbine like device in space spinning with KE and converting to Watts. Acceleration is constant?

I have a question that I can't seem to get my head around. I'm really rusty on my physics, but I'm sitting here trying to think this out, but I'm missing a really big part of the equation. So lets ...
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0answers
43 views

Radius dependence of Energy levels of spherical Quantum dots

I have frequently read in articles that the energy level of spherical quantum dots depends on radius. We simply match the wave functions inside and outside the particle and find the intersection of ...
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1answer
196 views

Does a rotating plank only acquire rotational kinetic energy?

I have another doubt with a Kleppner problem :(. A thin plank of mass M and length l is pivoted at one end. The plank is released at 60$^{\circ}$ from the vertical. What is the magnitude and ...
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1answer
26 views

Calculate amount of energy based on height of object

How can you calculate the amount of energy an object produces that falls from a particular height? Or water. In an eg i would like to know how can you calculate the amount of electricity water can ...
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2answers
120 views

Can matter be created from energy? [duplicate]

The small, hot, dense early universe the size of an atom was made up entirely of energy, it wasn't until after the expansion began and the universe cooled down some of that energy began converting ...
7
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1answer
211 views

Classical vs. quantum energy of the hydrogen atom

If I have an electron and a proton and calculate the classical energy which I get by bringing the electron from infinity to the distance of a Bohr radius to the proton, I get 27.2 eV, but the electron ...
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4answers
217 views

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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0answers
22 views

How is work done by a system in static equilibrium? [duplicate]

For a little colour: this came from my wondering why fork-lifts are hydraulically driven, rather than electromechanically. My question is this: why is it that some systems, while in static ...
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2answers
102 views

Does distance traveled by a vehicle after its engine has been switched off depend on its mass at all?

A vehicle moving with some velocity on a rough horizontal road finally comes to rest after its engine has been turned off. Intuitively, it seems a vehicle with greater mass would stop first because it ...
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1answer
34 views

How to calculate required energy to displace a pendulum?

How can one calculate the amount of energy needed to displace pendulum with given mass m and string length L to $\alpha$ degrees from resting position when acceleration due to gravity is known?
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1answer
63 views

Analogues of mass, space, or time? [closed]

I began wondering about this when working through this question: is there anything analogous to spacetime or matter? Both spacetime (note: most of what I know of about the concept of spacetime comes ...
0
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3answers
62 views

Kinetic energy relationships with momentum and mass [closed]

If I have some arbitrary particle, we will call particle 1 and another particle 2 that have the same momentum, yet particle 1 has half the mass of particle 2, how does the kinetic energy compare ...
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0answers
18 views

Is acceleration quadratic or linear outside of a gravity field? [duplicate]

So as I understand it: If you hit a wall at twice the speed you hit four times as hard? I often ask people this and everyone says "at twice the speed you hit twice as hard". $K=\frac{1}{2}mv^2$ is ...
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2answers
129 views

Why should energy have a lower bound but not an upper bound?

This question seems to be naive, but I really want some intuitive way of understanding the reason. Neglecting some trivial explanations, I have only one idea about this: the vacua state. Consider ...
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1answer
81 views

Kinetic energy in Lagrangian formalism

In reading Goldstein's Classical Mechanics (2nd edition) I came across a confusing derivation. Goldstein (Eq. 1-71) derives the total kinetic energy of a system of (classical) particles as: $$ T = ...
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1answer
80 views

Kinetic energy of a body rotating on another rotating body

Consider a body which can freely rotate with respect to the inertial frame, and a rotating disk whose axis is fixed in body frame. When applying the lagrangian method (does that make a difference?), ...
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0answers
84 views

If the energy of an ant is smaller than an elephant, does that mean the ant is more stable than the elephant?

I know that when a system is in its lowest level of energy, it is most stable. However, what if system 1 has lower energy than system 2, does it keep meaning so? Or do we need to examine their binding ...
7
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2answers
146 views

Why is salt so hard to remove from water?

Water molecules and various salt molecules are very different. However, it seems very difficult to separate the two. Once a salt is dissolved in water, an energy or chemical intensive method (like ...
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2answers
72 views

Non-additivity of energy (thermodynamics)

In page 15, Chapter 1 (Laws of Thermodynamics) of the book "An Introduction to the Study of Stellar Structure" by Nobel laureate S. Chandrasekhar, it is mentioned (in context of total energy of two ...
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2answers
104 views

Energy definition in special relativity

I'm going through the early homework assignments for my special relativity course and I've got myself a little confused about energy. I've got a basic understanding of what the 4-momentum is, having ...
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3answers
364 views

Why does water not evaporate in below 0 degrees?

I have learnt that, most objects still have energy in their atoms until the temperature reaches absolute zero. In other words, everything has energy around us. Now, that in mind if I go to antartica, ...
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1answer
43 views

Would half of electromagnetic wave be absorbed on first sensor?

If I would set up electromagnetic emitter that would emit one wave, but while it would be emitting it I would spin emitter 180 degrees at such speed that one half of wave would be emitted in that time ...
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1answer
59 views

Is it possible to generate electric energy from the radiation of radioactive materials

I wonder if it is possible to generate electric energy from the radiation of radioactive materials like nuclear waste? If it is then wouldn't that also mean that it could be used as an energy source ...
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1answer
90 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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1answer
75 views

what property of steam makes it the preferable motive fluid in jet ejectors? why not air or nitrogen?

I want to know what properties of steam make it the fluid of choice in steam turbines jet ejectors. I want to understand the mechanism of energy conversion in these equipment and hence understand ...
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2k views

Why isn't water running faster hotter?

I was running the washing up water this morning, and started to think about why the cold tap isn't hot, and why the water doesn't get hotter the faster it is flowing (if anything, the cold tap gets ...
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2answers
101 views

Conservation of energy in transformers

How does energy remain conserved in a transformer if emf is increasing, or decreasing? Does the current decreases to accomodate? Does Ohm's law still hold here? Although we know, Ohm's law is not ...
2
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2answers
4k views

What is the relationship between Force and Kinetic Energy?

I am an Middle-School (Grade 8) student, who is self-learning classical mechanics. I saw this equation from Classical Mechanics: $\vec F=m \vec a$, the following equation is pretty straight forward ...
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60 views

What is the energy operator and from where do we get it?

I am trying to learn Quantum mechanics from MIT OCW Videos about quantum mechanics. I have reached the 5th lecture. Please help me in understanding this: In the middle (At 32:08), the professor wrote ...
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1answer
27 views

Is watt unit depended on turbine speed

I'm new to electronics. I have a doubt. That is... Is watt unit depended on speed of turbine ? In my mind When turbine rotates fast the power in increase. Is it right ? Please help me. Thanks for ...
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1answer
42 views

Why is work not related to velocity?

A very simple question; why does it cost me more energy to very slowly lift a mass $m$ over my head compared to very fast? The definition of work does not state anything about velocity, only the ...
5
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1answer
109 views

What does the Higgs boson have to do with the uncertainty principle and quantum oscillations?

I was looking in New Scientist the other day when I saw something to do with the Higgs boson, energy levels, entropy, space/time, quantum oscillations and many other things. It was in a feature to do ...
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2answers
78 views

Energy of damped harmonic oscillator begins to increase with very large Q in numerical integration

I have numerically integrated the (reduced) homogeneous equation of a damped harmonic oscillator in order to see how the error propagates. $$\frac{d^2 X}{d\phi^2} + ...
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5answers
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How badly could someone be injured by concentrated sunlight?

Recently-ish, I stumbled across an interesting short story (by way of Science Fiction & Fantasy Stack Exchange) where a soccer referee is apparently incinerated by concentrated sunlight. Where ...
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3answers
2k views

Does an object's kinetic energy increase, decrease, or stay constant when it reaches terminal velocity while falling?

Does an object's kinetic energy increase, decrease, or stay constant when it reaches terminal velocity while falling?
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1answer
74 views

Conservation of energy and the 'crazy ball' product

Well I'm not sure how many people remember the crazy ball - a small ball made of rubber which bounced like crazy. What I noticed is that the ball seemed to bounce higher than the point from which it ...
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1answer
57 views

Energy density and Carnot cycle

For example, diesel has about 40 MJ/kg, what does it mean? Is that if we burn it we will get 40 MJ of energy per kg, but we can not get all of it to mechanical work? If that is the case, then why ...
2
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1answer
86 views

Does the Night Mode of the screen display (LCD) save more energy?

In some cases, we can enable the Night Mode (reversing the bright and dark color of the display; such as White Text, Black Background) for the screen display. LCD(Liquid-crystal display) seems to be ...
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1answer
68 views

Why do electricity generators have to work harder for higher loads?

Maybe this is a silly question, but why does, say, a gasoline-powered AC generator have to use more gas depending on the load? Let's say I have a 120VAC generator and either a 1A or a 10A load, and ...
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Why do we need high energy to explore small dimensions?

I am taking a quantum physics class, and for the life of me, I can not remember why we would need a vast amount of energy to understand the microscopic universe.