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.
I've had this question for a while now and I wonder if anyone can make sense of it. It's about two scenarios where the difference between them seems to contradict conservation of energy:
Scenario 1: In a vacuum chamber, there is a robotic arm, a box, a lower platform and a higher platform. At...
Sorry for my questions as an amateur interested in physics: If light changes its frequency during a long time of travel in space (vacuum?) for all observers (redshift) and therefore its energy decreases (E=hf), what "entity" absorbs this energy? I suppose the answer will be that the wavelength...
Start by finding the equilibrium position, so we have {4mgx}/{a} = mg giving us x = a/4, therefore the spring's length is 5a/4. Now the loss in EPE (and therefore gain in energy of the particle) between the bottom and the equilibrium position is clearly 4mg((a/4 + d)^2 , and then from the...
Hi PF, long time no see. Hope you are all well.
Recently I have come into a mental conundrum of a cosmological physical nature.
After doing some napkin calculations about the energy of celestial bodies and transforming them into mass via E=mc^2 I've found that said energy is by no means small...
So first I rewrote H as a matrix:
$$ H =
\begin{pmatrix}
a & b \\
b & c
\end{pmatrix} $$
And tried to find the eigenvalues/energies of H, so I solved
$$ det (H - \lambda I ) =
\begin{vmatrix}
a-\lambda & b \\
b & c-\lambda
\end{vmatrix} = (a-\lambda)(c-\lambda) - b^2 = ac - a\lambda -...
We connect the charged capacitor to the no-charged capacitor (consider the wires to be ideal R=0), the final energy is less than the initial energy of the system. Where is the lost energy? (see example blew)
I believe that this is due to context of application, but now, I'm starting to doubt myself. For example, a helicopter lifting itself has positive PE change. I really don't intuitively understand how this works. Can someone kindly explain this to me?
Hi.
If I drop an inelastic body, its potential energy first gets converted to kinetic, then to deformation energy. We use conservation of energy without taking into account the kinetic energy gain of the earth during the fall.
However, at first sight conservation of momentum seems to be...
In the Jan 6 Economist, there is an article about energy ("Britain needs an unprecedented expansion of the electricity grid") headed by this image. I assume that it is part of a power plant but I can't figure out what all those curved tubes are.
First, I thought, maybe heat dissipation but they...
I tried to calculate the energy of an H-Atom with the one electron integrals. I tried to solve them numericaly but it didn‘t worked. Thats why I am hear.
Hello everyone,
I am working on this problem and I think I almost solved it, but then I noticed, that I do not know what values I have for dn, n and dθ.
Can anyone help me with this?
I was initially under the impression that time crystals are in lowest energy state and neither gain or lose energy. But other sources suggested they might require a bump in energy after a while to keep going?
The first equation is when I use forces. The block is in static equilibrium, therefore the spring force should balance the gravitational force.
The second equation is when I use energy principles. Energy before compression = Energy at compression. The height before is x * sintheta, and the...
Let's say you've created a very large balloon that doesn't explode in a vacuum and filled it with a gas lighter than air. Next, attach the balloon to a basic electric generator with a very light rope and place the balloon in a vacuum tube. Due to the balloon's weight, it will descend in the...
is it even possible to split pu a proton and how much energy would it take to do that? i heard that it requires so much that it would make new a quark.
Why is (1/2)(mv0)^2 = 1/2(M+m0)gh not a valid equation for conservation of energy?
Isn't the energy from when the dart is shot the same as when the two masses move at speed v?
When E=mc^2 is rearranged using the substitution c=1/√ε0μ0
, and making mass the subject we get m=Eε0μ0
This equation basically says that mass is directly proportional to the energy contained in
an electromagnetic field. Does it not? Does this equation tell us that mass particles are made up
of...
Imagine an object, e.g throwing knife, spins in the air but not forced to rotate about a particular axis, i.e no rod impaling it and forcing it to spin about the rod. Then the axis of rotation converges to it's center of mass (CM) to minimize I. But there's nowhere for it's rotation energy to go...
Suppose in a different star system, a space shuttle sized spacecraft acquired a solar mass energy equivalent amount of kinetic energy, then passed through our solar system. While it was passing through the solar system would the craft’s gravitational effects be more similar to the space shuttle...
I've tried to solve this exercise but I haven't used one of the properties of the system (the displacement of the masses) so I don't know if I'm wrong about my procedure.
First of all, we (obviously) know that
$$
P=P
$$
And since we can express the power of a force in two different ways, we...
So if we set the damping constant ##\beta=0## that is if we consider an undamped oscillator the amplitude becomes infinity! What is the physical meaning of this phenomena? As we know energy fed into the system is proportional to ##A^2##. So does this mean that an infinite amount of energy is...
Absolutely no clue on how to even begin this question due to the exceptionally poor quality of our lectures, who has also flatly refused to give out any solutions, which I could have used to understand what is going on.
I assume the energy has to be obtained by using the eigenfunction equation...
Hello,
I am wondering if anyone can give me a hand.
I am looking for a unified expression for energy in rotating systems or wondering if one even exists.
Any help or equations you wish to share about the topic would be great.
Sorry I am quite new to physics.
Thanks
Suppose I have a protein PDB file and want to compute energy using the following formula from the coordinates in that file.
How can I do that?
Sometimes people suggest using the `CONECT` field for that purpose. However, some PDB files do not have this field.
Example: 4OSK.pdb (Crystal...
In a simple circuit consisting of a battery and a resistor, current will flow if the circuit is closed. Resistor uses the energy provided by the battery, creating heat with a power ##P = UI##, where ##U## is a voltage across the resistor and ##I## is a current through the resistor.
In my...
I registered yesterday in this forum with the intention of someone clarifying me how the Heisenberg uncertainty principle can explain the existence of virtual particles. More energy implies less lifetime is only possible if ΔE Δt = h/4Pi, but that's not Heisenberg's principle, the principle is...
A Beta-Type Regular Low Temperature Striling Engine being used to produce mechanical energy, where hot water at 350K is being used as fuel. What power should one expect theoretically?
I approach this by considering the four springs in parallel each with spring constant ##k## as one spring with four times the spring constant ##k' = 4k##. The car is dropped and at the moment its tyres touch the ground I assume that the spring is in its resting position. As the car continues to...
In his Chapter 13.3 (2nd edition), Callen gives the standard form for the virial expansion for the mechanical equation of state of a fluid as an exapnsion in powers of the molar volume ##v##:
$$P = \frac{RT}{v}\left(1 + \frac{B(T)}{v} + \frac{C(T)}{v^2} + \dots \right) \equiv P_{ideal} +...
I'm self-studying the mathematical aspects of quasi-local mass, or quasi-local energy (e.g. Hawking energy), and a fundamental question has been lingering in my mind for a long time: why does quasi-local mass provide us with a measure of the gravitational energy? In general relativity...
I converted 3.1eV into J, substituted into E = mc^2. Since the energy is the same, I got the same answer for both: 5.52*10^-36 kg. This doesn't seem quite right- I doubt that a photon and an electron have the same mass. So, when two particles have the same charge, does that mean they have the...
note:
m = relativistic mass
##m_o## = rest mass
v = velocity of the objectQuestion 1: If a particle is moving at relativistic speeds what would it's kinetic energy be?
I think it's ##K.E. = \frac{1}{2} m_o v^2## and my friend thinks it's ##K.E. = \frac{1}{2} \frac{m_o...
If I take a spring with clamps and I weight that system accurately. Then I compress the spring and clamp it thus giving it potential energy. If I now weigh the clamped spring I should see an increase in mass because of the added energy. Is this the case and something that could be proved in the...
A standard 12 gram cartridge contains both liquid and gaseous CO2 at 850psi. Assuming we are venting to atmosphere at sea level, how much energy can be extracted from the cartridge?
We know it will expand to 12 grams * 22.4 liters/ 1 mole (44grams) = 6.1 liters. But how much energy did...
In his classic textbook, Callen remarks that
I have labelled the claims (1) and (2). I am not sure about either. For the first, I have tried to proceed as follows (all equations are from Callen's second edition and all 0 subscripts are with respect to some reference state of an ideal gas):
I...
Suppose you stand on a spherical permanent magnet in space and you hold an iron ball in your hand, you can neglect the gravity force by this magnet mass. You stand and throw the iron ball upwards with some kinetic energy, the ball will eventually stops at some height because it is attracted by...
In Chapter 5 of his famous textbook on thermodynamics, Callen argues for the "equivalence" of the maximum entropy (Max-Ent) principle and the minimum energy (Min-En) principles. I quote from Callen first:
As far as I know (though Callen never makes this explicit in what, I think, represents...
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