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

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Anti-laser: How sure we are that energy is transported?

Reading this PE question can-we-transport-energy-over-infinite-distances-through-vacuum-using-light, a related question arises naturally: Is energy transported (by light)? -- (I did believed in this ...
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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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2answers
97 views

How does electric current generate thermal energy?

How does free electrons moving through a wire cause random vibrational motion of the positive ions?
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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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1answer
64 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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2answers
108 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
35 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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9answers
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Why is torque not measured in Joules?

Recently, I was doing my homework and I found out that Torque can be calculated using $\tau = rF$. This means the units of torque are Newton meters. Energy is also measured in Newton meters which are ...
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2answers
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How to calculate fuel consumption of car (mpg) from speed and accleration knowing mass, drag coeff and rolling resistance?

How can I calculate the current (instantaneous) mpg of my car if I know the speed and acceleration of the car? From reading various answers for the "car going level or up/down hill" question asked ...
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1answer
50 views

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

I know that when a system is in its lowest level of energy, it is stablest. However, what if system 1 has lower energy than system 2, does it keep meaning so? Or do we need to examine their binding ...
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2answers
93 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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1answer
48 views

Suggest why electrical power input P1 differs from power used P2

We have done an experiment heating water with a wire element and have determined it takes 21.5964 watts to heat 200ml of water to a specific temperature in 10 minutes. However the power of the ...
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2answers
60 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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1answer
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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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3answers
254 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
42 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
114 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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3answers
1k views

Work, Energy & Power - Body slides down a hemisphere

A small body of mass $m$ slides down from the top of a hemisphere of radius $r$. There is no friction between the surface of the block and the hemisphere. The height at which the body loses contact ...
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1answer
53 views

Energy Stored in a Capacitor with and without Dielectric

I have seen the equation $V = \frac {V_0}{K}$, but also the equation $V=\frac{1}{2}CV^2$. The values of C and V increase in the same linear ration with K (because $C=KC_0$). However, as the energy ...
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1answer
25 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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2answers
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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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1answer
64 views

What happens to gas molecules after ionization?

I know that gas molecules conduct electricity after they get ionized but what will happen if we keep increasing the voltage even after ionization? Will it explode? If it will then how much energy ...
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1answer
30 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?
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2answers
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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
39 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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1answer
25 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
38 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 ...
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Why does holding something up cost energy while no work is being done?

I read the definition of work as $$W ~=~ \vec{F} \cdot \vec{d}$$ $$\text{ Work = (Force) $\cdot$ (Distance)}.$$ If a book is there on the table, no work is done as no distance is covered. If I ...
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1answer
172 views

Integers, Energy levels, and wavenumbers for a particle in a 2D box

(This question is not about coding) I have built a little code in Python that allows the user to plot the energy vs the wave number of particle in a 2D box, depending on what values for the integers ...
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2answers
63 views

Electric potential energy and signs

I know that eletric potenial is negative near a negative charge and positve near a positive charge. But does this mean a small positive 'test' charge has a negative electric potential energy near a ...
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1answer
67 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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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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2answers
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Does quantum collapse involve a loss of information? Does it require energy as suggested by the Landauer Limit?

I read in the context of quantum computing or of the minimal energy required for computation that there has to be a minimum possible amount of energy required to change one bit of information, called ...
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3answers
111 views

Definition of force, kinetic energy and momentum

I've edited the post. Q1 and Q4 are the important ones but I didn't delete Q2 and Q3 since some older answers would not make sense anymore. To begin with, the formula of the kinetic energy $T$ is ...
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3answers
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Is “atmospheric geostationary satellite” feasible with current technology?

Meaning by "atmospheric geostationary satellite" a vehicle capable of hovering 30 km above Earth surface, hence insde atmosphere, for unlimited time, making use of air propellers, solar panels and ...
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4answers
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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.
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1answer
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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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3answers
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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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7answers
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Why can't we store light in the form of light?

We can store cold (ice), heat (i.e. hot water bag) and electrical charge (batteries). We can even "store" a magnetic field in a magnet. We can convert light into energy and then, if we want, back to ...
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1answer
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How do I describe and calculate the effect of an impacting object?

My lab studies the physiology of impact injury on biological tissues. I use a pneumatic cylinder to impart injury into a biological sample and then assess the molecular and physiological changes in ...
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2answers
170 views

What does it mean to “convert energy into time”?

In a recent article about creating electron-positron pairs by colliding photons in a laboratory, Andrei Seryi, director of the John Adams Institute at Oxford University, was quoted to said: It's ...
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4answers
304 views

What does the work on a current carrying wire in a Magnetic Field?

We consider that the force acting on a current carrying wire placed in a uniform magnetic field perpendicular to the length of the wire is given by $IBl$. If the wire moves by a distance $x$ in a ...
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1answer
55 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
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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 ...
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1answer
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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
34 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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7answers
755 views

How does heat actually stay kept in the carbon molecules in the atmosphere? [duplicate]

We have all learned that the earth is getting heat up because of the CO2 and CO molecules absorbing heat. However, how is heat actually kept in those molecules. When photons heat them up, their ...
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0answers
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Building free energy directly from Lagrangian

Energy can be built from Lagrangian when considering the symmetry of time $(\frac{\partial L}{\partial t}=0)$. Free energy is a generalization of energy when the system exchanges heat with the ...
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2answers
57 views

Calculating Quantum number from initial conditions

I have solved the particle in a box problem to get energy eigenstates and wave vectors: $$E_{n}=\frac{\hbar^{2} k^2}{2m} ,\hspace{1cm} k_{n}=\frac{\pi n}{L}$$ And now I am trying to figure out how ...
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2answers
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Energy of an EM Wave and its temperature and amplitude

I'm trying to understand why classical physics fails to explain black body radiation. I'm confused. According to Boltzmann, energy calculation for em wave is based on temperature. According to ...