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.
Hello I am a physiology student who is curious about the physics underyling blood flow and pressure. I have taken physics classes however at the elementary level the focus is on ideal fluids in systems with no friction. I would appreciate any answers or if you could point me in the right...
I'm thinking about how the energy is conserved when a E.M. wave pass through a conductor.
If a E.M. pass through a conductor, the electrons must move "oscillated", thus the energy from the E.M. wave is converted to kinematic energy.
Another way I see that is the E.M wave must generate a current...
I found an old article (https://journals.aps.org/pr/abstract/10.1103/PhysRev.137.B1379) which talks about conservation of energy in an expanding space. Apparently, the author found that energy is conserved at local scales (like the motion of planets in our solar system) as one would expect, but...
Assume two observers very far from each other, so far, that the accelerating expansion of the universe matters. (edit: But not outside of each others event horizons.) They will send light beams each other, and measure the energy of it. Also tie them together with a very long rope to fix their...
I was reading this interesting article [1] which talks about particle production in an expanding universe.
Usually this process is proposed to have occurred in the early universe, when the expansion was in the inflationary phase and it was so powerful that matter was created in particle...
Earlier today, I posted a question about the strain energy function.
I am happy with the answer (I love this group).
But the answer opened up a deeper question.
Many elasticity textbook posit the existence of a strain energy function:
And they make an additional assumption about its...
(If this is in the wrong forum, please move it)
Here is the potential energy of a spring
Here is the strain energy function in elasticity
The look alike -- I like that.
If we want the force in the spring, we take the derivative of V with respect to the displacement and make the result...
When an n-type material comes in contact with a p-type material to form pn-junction, electrons with the highest energy in the conduction band will diffuse to the p-side to reach equilibrium so the entire band structure on n-side will shift down relative to p-side as described in the following...
Hi, everyone! There are a lot of work energy conservation laws and I get confused which one of them summarizes all of them. Which one I should keep with me and rest should be easy to derive on spot ?
1. ##\Delta E_{mec}=0##
2. ##\Delta E_{mec}=W_{ext}##
3.##\Delta E_{mec} + \Delta...
I am working on a sanity check for capacity vs load and if anyone here has experience with off-grid solar, any feedback would be much appreciated.
The application is to run a fridge and a modem off-grid on a piece of land in New Mexico. I read that in December (worst case month) the area gets...
Apologies for an additional thread (could not delete the previous one which was not coherent). After reading this paper:
https://link.springer.com/article/10.1007/s10701-021-00464-7
"Fast Vacuum Fluctuations and the Emergence of Quantum Mechanics" Gerard ’t Hooft
I was struck by a general...
Hello, I'm hoping someone can help me understand a statement in Sakurai Modern Quantum Mechanics (3rd edition).
In particular, in the section that describes free particle in infinite spherical well (page 198, section 3.7.2), after the text has shown that for a given ##l## value, the energy...
We are all familiar with ladder operators, such as QM harmonic oscillators or in QFT to produce energy states which are interpreted as particles. But when a creation operator raises the energy level of a system, where does that energy come from?
From this post-gradient energy in classical field theory, one identifies the term ##E\equiv\frac{1}{2}\left(\partial_x\phi\right)^2## as the gradient energy which can be interpreted as elastic potential energy.
Can one then say that $$F\equiv -\frac{\partial...
There is an article written by astrophysicist Edward Harrison [1] which defends that energy could be extracted from attaching an imaginary cosmologically long string to a receding object from us in an expanding universe. He says that the energy extracted is potentially limited (in decelerating...
Energy = ##\frac{2000}{235}## x 6.02 x 1023 x 0.7% x 200 x 1 x 106 x 1.6 x 10-19 = 1.15 x 1012 J
But the answer is 1.15 x 109 J
I am off by a factor of 1000. Where is my mistake?
Thanks
I was reading an article by Edward Harrison, which tackles the problems of conservation of energy at cosmological scales.
At some point (point 2.4) he cites several article, including one by Rees and Gott, which he says indicates that the internal energy of a comoving volume (e.g. a cosmic...
It takes energy to compress an ideal gas, and that same amount of energy is output as heat. But we also gain the potential energy of the compressed gas. It seems to me that we are doubling up our energy.
Can anybody explain in simple, practical terms (to a humble mech engineer) how this works...
If I start with two, otherwise isolated, masses M and m initially together and do work to separate them then the work done, I assume, goes into the gravitational binding energy between them. Will the system of mass M and m have increased in mass due to this in accordance with e=mc^2?
I...
Sean Carroll has an article (https://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/) where he explains that matter can gain energy from spacetime expansion.
At the end of the article, he says: In general relativity spacetime can give energy to matter, or absorb it from...
This is in fact a shamelessly simple question to a point the reason it puzzles me is because it's too simple:
So basically you have a closed empty/hollow cylinder filled with either gas or even an ordinary solid ball...and then on the left side of the cylinder you put a force on the "fuel"...
This is my answer:
$$KE_{total}=KE_{centermass}+KE_{uppermass}+KE_{bottommass}$$
$$KE_{total} = \frac 1 2 (mv^2 + 2m(\vec {v} + \vec {wL})^2) $$
But, the solution manual says that the answer is this:
$$KE_{total} = \frac 1 2 (mv^2 + 2m(v^2+w^2L^2)) $$
I think he regard this composite body as...
This is not homework, just a question of curiosity. Something that came to my mind last night.
Say I have a magnet and a piece of iron. Say I use it to do weight training exercise. I stick the magnet on the wall and stick the iron on the magnet. Say it takes 100lbs of force to pull the piece of...
Firstly, what I'm about to do is to find the velocity of the mass soon after it doesn't touch the slide A anymore.
using momentum conservation, I got ##0 = mv' + MV'## with ##v'## and ##V'## are the velocity for mass C and slide A respectively immediately after they lost interaction.
Now, I...
Hey all,
I am working through some practice problems and am stuck at the following one:
"A cylindrical tank 10m high has an internal diameter of 4m. How much work would be required to fill the tank with water if the water were pumped in i.) at the bottom and ii.) over the top edge?"
Part i is...
What is the free energy and why is it so important? I realize there's different types but what is the underlying concept? Is a general principle of CM systems to attempt to minimise free energy?
Me again!
For a sci-fi story I'm working on, I've created a sci-fi technology called an Aneutronic Triple Alpha Fusion Reactor. It works via aneutronic fusion, in this case, fusing Deuterium with Helium 3, but it also mimics the triple alpha process found within stars to maximise fuel use...
Suppose there is a pressurized gas canister in space, at rest. With a mass "m" of gas inside of it at a pressure "P".
Next the valve of the canister is opened. The canister will accelerate in the opposite direction to the valve opening. When all the gas has left the canister, it will be moving...
About a year ago, I heard Leonard Susskind discussing how entangled black holes could create spacetime. As I was listening to Prof. Susskind describe the mechanisms for creating entangled black holes, and how these black holes might create their own spacetime, it occurred to me that if we were...
The energy of an electromagnetic wave does not depend on the frequency of the wave, only on the amplitude. Then why is light with higher frequency more energetic than light with lower frequency?
I already know the solution to this, all you do is set the height of the top of the trampoline to 0 and solve for initial velocity so the equation for the conservation of energy $$mgh_0 + \frac{1}{2}mv_0^2 + \frac{1}{2}kx_0^2 = mgh_1 + \frac{1}{2}mv_1^2 + \frac{1}{2}kx_1^2$$ becomes...
Hello! For the experiment I am working on we are using as the ion source an ablation target. We have a 1 inch coin of the material of interest (ytterbium currently) and we send laser pulses to it (we are using a 532 Nd:YAG laser). Can someone point me towards a paper (or tell me from their...
Hi
A theorem states that if V(x , t) ≥ V0 then <E> is real and <E> ≥V0 for any normalizable state. The proof contains the following line
<E> = (ħ2/2m)∫∇ψ*∇ψ d3x + ∫ Vψ*ψ d3x ≥ ∫ V0ψ*ψ
Can anybody explain why that inequality is true ?
Thanks
I am not against replacing fossil fuel, but we do NOT have a good solution yet. Why not build safer nuclear power plant? Or get into fusion power plant. I worked for a company as power of the Lawrence Livermore Fusion project back in 1979, still no result. Now they are fighting a losing battle...
I tried using the 109 J to convert to seconds but that didn't work. I also looked through the energy equations but nothing worked. I am not sure how to find time.
Hello physics researchers, teachers and enthusiasts.
I notice one little thing is confusing me in the derivation of Bernoulli's equation in the article, they write:$$dW = dK + dU$$where dW is the work done to the fluid, dK is the change in kinetic energy of the fluid, and dU is the change in...
My sign doesn't check out and I don't get why that'd be the case.
Forces that act --> ##F_{fr} and F_g##
derivation:
##\Delta K = W_{NC} + W_C (1)##
##\Delta K + \Delta U = W_{NC}##
##\frac 12 mv_2^2 - \frac 12 mv_1^2 + mgy_2 - mgy_1 = W_{NC}## NOTE: ##y_2## assumed to be datum line so ##y_2 ==...
Hello there, I have tried the problem but don't get a different of 6g's as I am supposed to. I am not sure whether I interpreted the problem in the correct way, but I would love some feedback/hints on what went wrong in my solution, thanks in advance.
Solution:
SITUATION DRAWINGS + FBDS
so...
so I haven't looked at the solution yet, but I know that a 100% the velocity needs to be bigger, but analytically, I get a - sign instead of a + sign as you'll see at the final square root.
So for the first 15meters of the motion all you should know is that ##v_1 = 10.458 m/s##.
for the 2nd...
this is an easy problem but would it be possible to consider car-car system. What I did on paper was carsystem and because they have the same properties(mass en speed) multiply by ##2##
solution for car-car-earth system I assume is the following if it is possible?
solution for car-car:
law or...
I am writing a military SF, and wonder, what could be the most realistic things, that are close to the old SF concept of energy shields.
So far, i wrote that a small mecha uses a handheld plasma shield against an incoming missile. Like explosive reactive armor, it meant to shatter the...
So in this picture friction is also assumed, but if we assume friction as an energy don't we need to consider the system to be earth, roller-coaster car, roller-coaster itself(due to friction force)? I actually still had this question from a previous coverage of this material lol...
I just...
Electrons flowing through a resistor are dissipating electrical energy. The electrical energy is transported from the battery to the electrons along the curved field lines of the Poynting vector. It seems like a meaningful idea that electrical energy necessarily travels from the source to the...
While reading this thread on Stack Exchange... https://physics.stackexchange.com/questions/113092/why-does-a-system-try-to-minimize-potential-energy ... a question came to mind : -
Say an object is launched away from Earth at a velocity greater than the escape velocity. This system will not end...
Hello :
i was watching the news , and it was all about how Europe will start the coal factories again for energy generation
had a question related to reduction of coal consumption for energy generation
1 ) could we use coal fine particles instead of chunks of coal that will burn more...
A point charge of value q=8uC is released from rest at a point 1.5m away from the center of the axis of a ring with uniform charge density 3uC/m. The ring has a radius of 10 cm. What is the kinetic energy of this charge when it is 4.5 cm from the center of the charge ring, considering that it is...