In physics, energy is the quantitative property that must be transferred to a body or physical system to perform work on the body, or to heat it. Energy is a conserved quantity; the law of conservation of energy states that energy can be converted in form, but not created or destroyed. The unit of measurement in the International System of Units (SI) of energy is the joule, which is the energy transferred to an object by the work of moving it a distance of one metre against a force of one newton.
Common forms of energy include the kinetic energy of a moving object, the potential energy stored by an object's position in a force field (gravitational, electric or magnetic), the elastic energy stored by stretching solid objects, the chemical energy released when a fuel burns, the radiant energy carried by light, and the thermal energy due to an object's temperature.
Mass and energy are closely related. Due to mass–energy equivalence, any object that has mass when stationary (called rest mass) also has an equivalent amount of energy whose form is called rest energy, and any additional energy (of any form) acquired by the object above that rest energy will increase the object's total mass just as it increases its total energy. For example, after heating an object, its increase in energy could be measured as a small increase in mass, with a sensitive enough scale.
Living organisms require energy to stay alive, such as the energy humans get from food. Human civilization requires energy to function, which it gets from energy resources such as fossil fuels, nuclear fuel, or renewable energy. The processes of Earth's climate and ecosystem are driven by the radiant energy Earth receives from the Sun and the geothermal energy contained within the earth.
Can energy be defined as an entity? The ability to do work is abstract, so is E=mc^2. It seems like energy is a catch-all phrase for something we can only describe in terms of other physical realities.
Energy is equal to Planck’s constant times the number of waves in 1 sec. The time scale for electronic excitation is far shorter then one second. So when we talk about the excitation of an electron from a lower level to a higher level occurring at a certain energy, are we talking about the...
Hello guys, I am designing a 1052 kwh solar farm with 2844 panels in Wales. These panels have to supply energy to a train station but I get minors coverage of the energy required if I do the following calculation which is based on the average sunshine of hours per month. What do you think about...
Hello everyone, I have found this on internet but I don't get the calculations. Can someone do the calculations and show me that the annual consumption is 600 kWh is you use a 200 Wh computer for 8 hours?:
A complete desktop uses an average of 200 Watt hours (Wh). This is the sum of the average...
I understand the idea of a fictitious force. What I am confused about is the energy/potential associated with it.
For example, if a cylinder of water is rotating, there apparently exists this centrifugal potential energy, which is obtained by integrating mrw^2 dr. Why is it that the...
I have some doubts with respect on how the functional derivative for the kinetic energy in density functional theory is obtained.
I have been looking at this article in wikipedia: https://en.wikipedia.org/wiki/Functional_derivative
In particular, I'm interested in how to get the...
I was thinking about the Gravity-B probe and the rotation of the satellite due to the Lense-Thirring effect. I was imagining that the satellite, once in orbit, was aligned to a distant star using retro rockets effectively rendering it non-rotating relative to that star. That being said, once...
I've been researching pem electrolyzers, but still don't understand how to mathematically express how platinum reduces the activation energy necessary to dissociate H2O. I've seen the Arrhenius equation solved before, but didn't understand how to get the values for it. Here are the operating...
Hi,
I have to find the magnetic energy inside a coaxial cable of inner radius ##a## and outer radium ##b##, ##I = I##
By using Ampere's law
if ##r<a##
##B = \frac{\mu_0Ir}{2\pi a^2}##
if ##a<r<b##
##B = \frac{\mu_0I}{2\pi r}##
if ##r>b##
##B = 0##
Then, the energy in a magnetic field ##E_b...
Of potential and kinetic energy in their various forms, in their own reference frames, which involve motion? Heat, light, nuclear, kinetic, etc., seem to involve motion. Does potential energy, in any way whatsoever, involve motion? Thermal does. Does nuclear energy involve motion? Seems to...
I have completed part a, from which I got the expression: Cv = 3KTn/(T_f)
For part b, the first term is the electron contribution and the second term is the phonon contribution.
I'm stuck on how to estimate the fermi energy for the potassium metal. I'm thinking I only need to consider the...
Hello!
I've come across this forum looking for an answer to an odd question related to energy production. I have no intention of creating infinite energy so don't worry.
Imagine a very strong balloon with a cord wrapped tightly around it. The balloon expands pulling the cord which spins a...
Textbooks always give an explanation for why electrons move between energy levels in atoms with an explanation something like this:
'An electron can jump to a higher energy level if it absorb's energy which exactly matches the difference between final and initial energy level'.
My question...
Well, internal energy is the sum of the kinetic and potential energies of all the molecules within a given mass of a substance; this energy is associated with the random, disordered motion of the molecules.
An example of internal energy is compressed gases; since gases occupy the total volume...
Yes, heat can flow into a body without increasing the mean kinetic energy of its molecules. Transferring heat energy to an object will raise its internal energy, this will not necessarily cause an increase in temperture. Specific latent heat is the energy required to change the state of one...
Is the purpose of the 0th, 1st & 2nd Laws of Thermodynamics simply to legitimate the thermodynamic properties of Temperature, Internal Energy & Entropy, respectively?
It seems that all these laws really do is establish that these properties are valid thermodynamic state properties and the...
I was going to put this in the homework forums, but on second thoughts it's more conceptual so perhaps here is better. It's about problem 4, chapter 6 of Wald. Part (a) is fine, $$u^a \nabla_a u^b = \frac{\xi^a}{(-\xi^c \xi_c)^{1/2}} \left( \frac{\nabla_a \xi^b}{(-\xi^c \xi_c)^{1/2}} +...
Hello. Questions: Are antimatter, dark matter, negative mass confirmed that they exist and exhibit as phenomena? What about dark energy and negative energy? Do these types of matter behave as wave also? Do they exhibit such behaviour? About those types of energy i said, can they be transformed...
First, in section 20.4, after listing all the things gravitational potential energy does not do, they say the equivalence principle forbids it being localized. I thought I understood the equivalence principle, but maybe I don’t. Any comments explaining that would be appreciated.
Second, they...
If a system is in an eigenstate of the hamiltonian operator, the state of the system varies with time only with a "j exp(w t)" phase factor. So, the system is in a "stationary state": no variation with time of observable properties.
But the system could in theory (for what I understand) be...
We know that energy can be converted from one for to another , but how does it do that?
How exactly does energy interacts with the quantum particles or with strings for that matter?
How much energy is required to double the radius of a uniformly dense stellar object? Express the answer in terms of mass and the radius of the object.
I solved this problem easily using Newton's second law, but I had problems trying to use mechanical energy conservation to solve it.
How I solved using Newton's second law:
##\text{(part of the rope that is on the left)}\, m_1=x\rho g,\, \text{(part of the rope that is on the right)}\...
Am i right
Is internal energy for engineering just the sum of energy stored with a system of a substance. which is only affect by heat and work coming out of the system
If you search on-line for "efficiency of a black hole" you will get several discussions suggesting that the efficiencies of converting mass to energy are from 6% for non-rotating black holes to 42% for the fastest rotating black holes. I would like to know exactly how black holes convert some of...
Remind me please? In a three level system, with discrete energies E0,E1,E2: would light-shift (Stark shift), applied due to an external electric field, change the values of E1 and E2 by the same \Delta E? Or would \Delta E1 be different from \Delta E2?
I know the answer would be yes, but why?
In class, I learned that energy is scalar and cannot be negative (at least in undergraduate class). Thus adding two sources of energy should result in a higher level of energy in general. But here for wave, if we have 2 waves that do destructive...
Hello there,
I am interested in renewable or clean or new energy sources. What branch of physics that I need to focus on in order to get a deep understanding on this? Also, what prerequisites do I need?
p.s. I am a self taught student, so I don't have any academic advisor
In Principles of Lasers by Svelto, while deriving the Planck radiation formula, equation 2.2.3 says $$I_{\nu} = \frac {c_0} {4n} \rho_\nu$$
where ##I_\nu## is the spectral intensity at some hole in the cavity wall (energy per time per area per frequency),
##c_0## is the speed of light in...
Hi,
Could anyone please give me a little advice.
If we look at a disc brake on a vehicle, the disc brake pads apply a friction force on the disk rotor which causes the kinetic energy of the moving vehicle to be turned into heat.
Does this heat reduce the reactive force experienced on the disks...
Hello everyone. I have a question that as simple as it looks it is making me doubt if I answered the correct solution.
A room is illuminated by 12 double fitting 85W fluorescent lights and I got to calculate the energy consumption.
I multiplied 12 x 2 because it says it is double fitting but I...
Hello. Be v grateful any assistance with this.
Question is energy to haul 2000kg 4 metres up a 1 in 100 incline with 300 Newtons friction
Answer is given as exactly 1.98 kJ.
The only figures I can see that relate to anything here are 2000kg minus 10 = 1980, and 1:100 is 0.01 which times...
Assume that a contraption with loosely suspended internal weights is fixed to the body of a vehicle that is moving in free 3D space without gravitational sources nearby. Given the position and orientation of the vehicle as functions of time, how can one tell whether it is possible for the...
Summary:: Doubt in a spring exercise
Text of the exercise "a mass of ##m = 0.4 \ \text{kg} ## is attached to a spring and it oscillates horizontally with period ##T = 1.57 \text{s}##; the amplitude of the oscillation is ##d = 0.4 \text{m}##. Determine the spring constant, the total energy of...
Hi there,
I am doing a mechanical energy question. I think the solution is simple but I'm stuck on an algebra step.
This is the solution but I am really not sure how they have simplified down to Va.
For example I tried to factor out the m resulting in
1/2mv^2=m(1/2va^2+gh)
Then I cancel...
Hello everyone. I need to calculate the annual energy consumption for a total of 6 electric devices. I got the following information:
The A operation consumes 177 kWh 5 times a day for 6 devices for 250 days a year (9 operational hours daily)
Each device consumes 113 kWh daily for 250 days a...
I am considering a system that includes a pn-region with N first then P, then a superconductor, but I am not interesting in the effect of the modes present due to the confinement of the p-region of the system on the conductance (from electrons to holes). How do negate these energy modes in the...
This is my understanding of the law of conservation of energy and the role non conservative forces factor into it. Could someone confirm if I have this right or explain where I am going wrong if I am? I would appreciate it.
With the law of conservation of mechanical energy, ΔKE+ΔPE=0. This...
Hello. I have a question related to capacitance.
here is another mechanical solution to harness wave energy.
Can changing capacity of the capacitor be used to harness wave energy?
Let's say we envelope conductive plates in plastic and submerge them
in the ocean and the water in between them...
I started of by trying to find the work for I got stuck because I did not know how to solve for the Force. I solved for the distance by doing 3=d/5s which gave me 15m. but then I couldn't figure out where to go next in the problem because I don't know how to solve for (f) so an explanation would...
This is not my homework. I took it upon myself to answer a textbook question for mental stimulation. I wanted to know if someone can verify if these were the correct values that needed to be solved for, process, and final answer, and if not, what needed to be considered.
For the initial...
I've come to a grinding halt with this and I can't see a way forward.
Can someone please take a look at what I've done so far and let me know if what I have done is OK and then if it is, give me a hint on how to proceed.
First up,
Is ## u \cdot \nabla \cdot T = u_\alpha...
In Robert M. Wald's General Relativity he writes on page ##61##:
The energy of a particle as measured by an observer - present at the site of the particle - whose 4-velocity is ##v^a## is defined by
$$E=-p_a v^a$$
Thus, in special relativity, energy is recognized to be the "time component" of...
In this problem i don't find any way to obtain de kinetic energy in KJ/Kg because when i resolve the kinetic energy formula the result its:
1/2 (1300 kg/s) (9 m/s)^2 = 5850 kg * m/s (i don't obtain m^2/s^2, so KJ/Kg its not possible)
In the potential energy (w) part i obtain this:
m*g ( i don't...
This questions is hovering on my mind from a long time. Why would something which does not have life would want to be in such a beautiful neighborhood, while the world is so much disordered. What causes them to be in that regular array and how they choose which crystal structure is suitable for...
Hello,
I was wondering if someone could help clarifying this question.
The question asks to estimate the energy state difference between the vibrational ground state of S0,v=0 and the first excited vibrational ground state S0,v=1 of the spectra below.
The given solution: S1,v=1 -> S0,v=1 at...
Let us attempt part C first, which is to find the total energy of the entire system.
I can definitely find an expression for the force, as given by Coulomb's Law. However, why should I integrate this force from infinity to d, where d is the distance of the external charge to the centre of the...