Questions tagged [energy]

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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43 views

Why does kinetic energy below molecule bond energy break bonds?

I was thinking about why bullet can break molecular bonds when it hits solid target despite the fact that the kinetic energy of the individual atoms that make up the bullet is less that the molecule ...
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Why is my solar panel more efficient as the temperature increases, rather than less efficient?

I have recently performed an experiment in which I placed a solar panel inside a closed box, together with a heater and a lamp (60W). I increased the temperature using a heater from 20ºC to 50ºC. The ...
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How do electrons lose their kinetic energy in ideal wire?

Electrons keep accelerating due to the electric field (produced by the battery) along the circuit. So electrons gain kinetic energy, hence their drift velocity changes. But this is not the case: ...
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What does this mean? World consume 14 trillion watts of power

I am not very clear about this statement. Does that mean in every second we are consuming that much energy?
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Why is there energy being spent / work being done in a static system?

Sorry that I don't have pictures. Imagine I have a steel circle, like a hula hoop. On opposite sides of that circle I attach two springs, then stretch them. They meet in center where I hook them ...
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In special relativity is mass just a measure of all other energy than kinetic?

The energy momentum equation in special relativity is: $$E^2=(pc)^2+(mc^2)^2.$$ and it holds for a moving but not accelerating object. One special case is the massless photon: $$E=pc.$$ And another ...
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How much energy does it take to form a plasma channel with a laser?

The usage is for something like this https://en.wikipedia.org/wiki/Electrolaser I know that the laser is powered for an instant in which a plasma channel is formed for the electricity to flow through,...
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Quantization of angular momentum of system of particles

Suppose there is a system of particles interacting with each other. Is it the angular momentum of each particles which would be quantized as $\sqrt{n(n+1)} \hbar$ or is the angular momentum of the ...
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1answer
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Proper definition of Internal energy

In Internal energy of a gas ($U$), we have to include ALL types of energies possible like $KE$, bond energies, nuclear interaction energies, etc.., However we have derived that $U = (f/2)nRT$ from ...
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Is this dark energy? [on hold]

Consider a particle travelling near the speed of light towards a planet- relativity states that the space according to the particle shrinks between the particle and the planet as the particle ...
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How much energy would it take to blow up the Earth?

There is a common statement running around that we as a species has enough nuclear weapons to blow up the earth several times over. What I want to know is: by how many orders of magnitude is that a ...
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Energy consumption from acceleration

I have an interesting problem. I have a machine which has to lift 35 kg (this is the total mass of the object and the lifting arm). The lifting is done by a servo motor. Now I want to calculate the ...
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Entropy change of the surroundings

My textbook says: $\displaystyle\Delta S_{surr}=\frac{q_{surr}}{T}=-\frac{q_{sys}}{T}$ So far, so good. It then goes to say: $\displaystyle\Delta S_{surr}=\frac{-\Delta H_{sys}}{T}$ [at constant $P$...
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Varying of momentum for constant kinetic energy

How is that If the momentum of the particle is constant with time, its kinetic energy ($E_k$) should also be constant with time a true statement but the converse is false... When momentum is ...
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Energy contributions of Hamiltonian density

In Lancaster and Blundell, Quantum Field Theory for the Gifted Amateur, p.99, Hamiltonian density is \begin{equation} \mathcal{H}=\frac{1}{2}[\partial_0\phi(x)]^2+\frac{1}{2}[\nabla\phi(x)]^2+\frac{...
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Why does kinetic energy increase quadratically, not linearly, with speed?

As Wikipedia says: [...] the kinetic energy of a non-rotating object of mass $m$ traveling at a speed $v$ is $\frac{1}{2}mv^2$. Why does this not increase linearly with speed? Why does it take so ...
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How would the angular velocity of the rod change if it slipped on the table?

I wanted to consider a second case of my homework assignment. We were asked to solve the question: A uniform rod of length b stands vertically upright on a horizontal plane in a position of unstable ...
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Difference between coherent and incoherent energy transfer (e.g. in photosynthesis)?

Several authors distinguish between incoherent and coherent when describing the energy transfer mechanism that forms the basis for photosynthesis. (e.g. Clegg & Sener 2010 and Keren & Paltiel ...
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Derivation of the K.E. formula without the work-energy theorem (or proof of the work-energy theorem without the kinetic energy formula)

All of the derivations I have seen for the kinetic energy formula have relied on the fact that work is the change in kinetic energy, something like the one found here: How to prove equation of kinetic ...
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If the heat capacity of an object changes does the internal energy or temperature of the object change?

Consider a spherical particle of material B contained in a spherical shell of material A. The thermal expansion coefficient of B is greater than that of A so that when the object is heated an internal ...
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Car Max Range Equation

In space engineering, thanks to the rocket equation, if you know some properties about a rocket (payload, fuel mass and specific impulse) you can compute the theoretical maximum distance the rocket ...
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1answer
130 views

charged plasma and ion grid in interaction in ion thrusters

I was just wondering ..... In this Image of an ion thruster, when the positively charged particles pass through the grids, wouldn't they just bombard the negatively charged grid(a fraction of them). ...
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1answer
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Reduce temperature of fluid inside an isolated system without dissipating heat

Suppose you have a perfectly isolated system filled with a fluid, which cannot transfer heat nor matter to the external environment. Suppose you want to reduce the temperature of the fluid within ...
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Best way to apply force to all sides of a cylinder [on hold]

Im looking to apply force to all sides of a Cylinder from the inside with as much force possible without eruption.
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Stationary State of Quantum Mechanics [duplicate]

Why for every normalized solution to the time-independent Schrödinger equation $E$ must exceed the minimum value of $V(x)$?
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3answers
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COSMIC ACCELERATION

Please forgive a probably naïve question from a lay person. I understand that galaxies are all moving away from us in every direction we look. And for any given distance the speed is the same. And ...
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Energy loss caused by a negative work

Let's supposed a box is sliding on a friction-less surface, so it has some KE at this point, and let's imagine an external force is being applied on the opposite direction of the displacement of the ...
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The strict definition of partition function in continuous system

I am confused about the definition of the partition function. From the class of statistical thermodynamics, I've learned that the partition function for a system with continuous energy can be ...
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How does conservation of energy work?

I understand that the law of conservation of energy states that energy cannot be created or destroyed, it can only change from one form to another. This means that the total energy before a certain ...
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Instantly freeza lava [closed]

If you could magically freeze lava, what would be the temperature and energy output of your spell (in KJ/Tons)? In this case the lava is 20 meters in diameters and instantly spawned beneath your feet.
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1answer
209 views

Using Helmholtz Free Energy to Calculate Liquid Density

My objective is to find an equation of state (EoS) for density, i.e. density as a function of pressure, temperature and concentration, for aqueous acids, bases and salts. A StackExchange user ...
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Energy of a light wave

I know that the energy of a photon can just be found from the equation E = hv. However, if we measure light as a wave, can the energy be found from the amplitude rather than the frequency, like you ...
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Elastic Collision And Momentum

The question I am working on is, "Two blocks are free to slide along the friction-less wooden track shown below. The block of mass $m_1 = 4.98~kg$ is released from the position shown, at height $h = 5....
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1answer
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How does energy flow in a circuit?

I read some information on a certain blog saying that energy does not flow inside the wires of a circuit, it propagates in the form of an electromagnetic field outside the wires and straight into the ...
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How does the photon energy formula $E=h\nu$ mean the quantum nature of energy?

The frequency v can be less than 1. So the energy is starting from zero, and is continuous. The black body radiation is also continuous spectrum given an arbitrary temperature T.
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How work interferes into law of conservation of energy problem?

A 10kg block slides down a hill that is 200m tall as shown in the figure below with an initial speed of 12m/sec. a) What is the speed of the block when it reaches the bottom of the hill at position ...
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How can one prove the existence of potential energy?

Potential energy always seemed weird to me. Like it's not a real type of energy, just something made up so that the Law of Conservation of Energy stays true. So I want to know if the existence of ...
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Electron falling into proton approaches infinite kinetic energy why?

Foreword I believe this question to be different from the usual "Why don't electrons fall into the nucleus" because this A: asks about the details of explanations for why electrons don't fall into ...
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2answers
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“Energy transfer” and “Energy transport”

Are the terms "energy transfer" and "energy transport" sometimes or always interchangeable? My own surmise is that the term "energy transfer" is slightly more general: "energy transport" refers to ...
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Where do electrons get their ever-lasting circulating energy?

We all know (or maybe know) that to move, we need to spend energy. If you want to drive a car, you gotta spend gasoline. We also know that energy can't be created (first law of thermodynamics, and ...
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Rigid bodies and inelastic collision

If two rigid bodies collide - how the collision can be inelastic? where the energy goes? If the energy transffered to heat, doesn't it contradict that the bodies are rigid?
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Question about $E=mc^2$

When a nuclear reaction happens, the amount of mass disappeared satisfies $E=mc^2$. However, the reaction will stop at a certain point, there is no way to make the whole thing disappear into energy. ...
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Energy required to accelerate from different reference frames

So I've recently been studying relativity a lot trying to understand it and I feel like I grasp most things conceptually but I have one issue I've been trying to understand for the last couple days ...
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What frequency is the scratching of finger nails on a blackboard?

This is the frequency/intensity that sets my teeth on edge. Does anybody know what frequency (roughly) it is? I am guessing it is near the top of normal human hearing, 20kHZ, but I'm not sure if ...
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1answer
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Work done by static friction in Rolling

In rolling without slipping, I understand that the velocity of the point where static friction with the ground is 0, and therefore static friction cannot do work. However, from newtons laws, an object ...
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How can I find the Helmholtz free energy from the Sackur-Tetrode equation?

I have the Sackur-Tetrode equation for the entropy: $S=k_{B}N[ln(\frac{V}{N}(\frac{4\pi m}{3h^{2}}\frac{U}{N})^{\frac{3}{2}}+\frac{5}{2})]$ May I isolate the U in this way? $U=\frac{3h^{2}N}{4\pi m}...
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3answers
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What is beyond Gamma Rays and Radiowaves in the Electromagnetic Spectrum?

The electromagnetic spectrum is commonly refered to as consisting of; Radio-waves, Microwaves, Infrared, Visible Light, Ultraviolet, X-rays, Gamma Rays - of increasing frequency from left to right. ...
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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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How to measure (heat) energy used?

Before I start with my question, would like to highlight - the last time I delved into this topic was 13 yrs back during my schooling courses. But the enthusiasm never died. Coming back to topic - I ...
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Energy quantization

Why does a free particle give rise to a continuous spectrum of energy eigenvalues while a particle in a bound potential gives rise to a discrete spectrum?