Works Definition and 447 Threads

I am puzzled by the fact that a "single-particle" Hamiltonian (in the annihilation and creation operator form) may be used for a multi-particle case (non-interacting particles) or that (only) a "two-particle" Hamiltonian (in the annihilation and creation operator form) may be used for a...

Hi, I'm slightly confused with the Aguirre-gratton model, and was wondering if someone could explain using simpler terms? I have read from : http://www.preposterousuniverse.com/blog/2007/04/27/how-did-the-universe-start/ " Aguirre and Gratton have presented a proof by construction that such a...

Could anybody explain what happens at the molecular level when one of the two bodies in a contact starts moving w.r.t other, i mean in this process what causes kinetics friction force, i tried myself to think of it but i could not come up with any, so please help me.

How spiral torsion spring (used in mechanical watches to store energy) works? physics behind it ? ... I googled it but haven't got a clue. Where should I look for proper and detailed info.

Hi guys! I need help about explanation how to work turbojet. I have read about turbojet on Wikipedia and I know how to work turbojet in base.But some things are unclear to me. I would be thankful if someone explanation how to calculate elements about turbojet. Thanks!

I heard about electromagnetic pulse, that it can cause damage to electronic devices if one intentionally shots out such a burst. But I wonder, wouldn't that person him/herself be affected by the pulse? I mean, the pulse would work like a lighting. So that person could even die by his/her own...

Homework Statement 2. Questions I want to know how this proof works, but there are several things I don't understand. (1) How does the ##k\epsilon## appears? ##k## is the lipschitz constant, but what about ##\epsilon##? Is the author taking ##||x-y||<\epsilon##? (2) What does the...

Clearly math is a product of human thought. But is there a prior reason for this? A possibility is that math is a byproduct of basic information that we obtain from nature, where that information come in the form of ideas in which we have to sort out into something more rigorous. We absorb...

In a positive feedback amplifier, as I understand, output of the amplifier is fed back into the input of amplifier, essentially creating a loop. My question is specifically, how the loop does not go in an infinite cycles ? what prevents it from going into an infinite loop ? How many cycles...

Is there any experimental proof which shows that the force of gravity works at Planck length? Has it been verified already? Is it verifiable?

I've seen a little bit about the gravity light. I think it works in a simple way, a weight at a certain height has gravitational potential energy depending on how far the weight will fall, this quantity represents the total energy we have at our disposal to power a light. Now we normally think...

I am trying to understand how refrigerator works from the thermodynamic perspective. I've read many articles and watched several youtube videos but still trying to figure out following stuff. 1. What exactly is the purpose of compressor? Ok it compresses vapor and thus increases it's pressure...

Hello I found some webs, but I would like to know a bit more https://en.wikipedia.org/wiki/Electroejaculation http://www.ivf-infertility.com/ivf/ejaculation.php "is to directly stimulate the seminal vesicles." I don't know how exactly works in "natural conditions", but it seems to me that the...

Hello How mosquito CO2 detection system works? I found that the detection is made by npa neurons, but nothing is said about how the detection occurs (so, CO2 enters the neuron, and what happen next?) https://www.nih.gov/news-events/nih-research-matters/how-mosquitoes-detect-people Thank you...

Homework Statement [/B] Inside a sperical dielectric mass there is a electric dipole on the center of the sphere. The sphere has radius a. This dieletric sphere is inside and on the center of a conductive spherical shell of radius b. The problem asks to find the potentials and then the...

Hi everyone. I have a question with a DLC (Diamond-like-carbon) coating. In many papers, the DLC coating without hydrogen (a-C or ta-C) shows very good frictional properties and wear resistance with water lubrication. I'm studying on eco-friendly engineering, so I surprised that water can be...

launching a missile from the water, how the ballast stability works?

I'm a physics teacher and I've found it hard to explain motor's working to a couple of students.

Hi All, what is the reason why very close to an electromagnetic source (Fresnel Region), the wave impedance Z0 in free space for electric field and magnetic field is not the same? Z0 for magnetic field increases and for electric field decreases by increasing the distance from the source...

The higher the dielectric constant, in a sense the more mobile the charges are in side the material. So a higher dielectric constant will cancel more of the field inside of itself, and a metal will ideally cancel out all of it. But what happens on the other side of the material? Does it re...

Guys, how does blood glucose sensor works? I am particularly interested, how does glucose is adsorbed in the sensor, how does it converted into electric signal?

I've just looked through different kinds of sites and I can't seem to find any specific answers. I need it for our technical report. If you guys know any links, just quote it here. I just really need your help

I've got to explain how spin art works to some 5th graders tomorrow. Basic setup: Paper is attached to center of a horizontal disk. Paint droplets are placed at different places on the paper. Disk is spun which causes paint to produce a pattern flowing away from the center of the disk/paper...

I'm reading Gerald Folland's "Quantum Field Theory: A Tourist Guide for Mathematicians" and I'm up to Section 6.2 which is called "A toy model for electrons in an atom". He has a nonrelativistic particle of mass M and a scalar field with quanta of mass m and the state space for the particle is...

Hello Everyone, I would like to understand entanglement a little more clearly. My understanding is that two or more quanta (for example photons) that are entangled become a single entity. Entangled or not, there is always a single and total wavefunction that describes the system but in the...

There is an explanation of how a battery works that says that in a battery circuit, the electrons do a complete loop and, given enough time, they can return to their starting point. This theory says that when the electrons arrive in the positive terminal and they lost all of their potential...

I came across a guy claiming that the "best approximation" for the natural logarithm of a number is this: ln x=2^n*(x^(2^-n)-1) Oddly enough, it seems to work rather well! I don't really get why it does... I also don't know if it has a limit, I couldn't test it as I don't have access to my...

What exactly is happening to the electrons inside the wire while it is moving quickly downwards within the Magnetic field? Why do electrons move in one direction if the wire is being push down? I don't care what direction electrons move... I want to know WHY they move in one direction?

Halfway through my thesis on a mach 2 ramjet, and I unfortunately realize that I need 50-72 CFM to test it. The only ACs I have are 2 CFM portable pancakes. Is it possible to run say a 25 CFM AC at 50 CFM for a short period of 10-60 seconds? Is there a quantitative way to find how long the AC...

I'm trying to decide which sort of engineering I want to do. I am leaning towards mechanical, what are examples of environments where mechanical engineers can work? Thanks.

Hi guys I am a new member here so I am looking for feedback on the quality and clarity of this post as well as a solution to the problem. If there are any suggestions as to how I can improve the format or wording of the question I am always looking to get better. On to the question, I am...

Homework Statement Homework Equations F=m*a ΣF(n-direction)= m*a(n)= m*(v^2/ρ) ∑F(t-direction)= m*a(t)\ Ffriction= Fn*coefficient(of friction) The Attempt at a Solution So I tried solving this question and apperently it is way easier than I thought. So I thought the kinetic friction has a...

There are several unreasonable assumptions in the formulation of the Prandlt Mixing Theory. However, it works reasonably well for simple 1-D flow. An attempt to explain why is given by Davidson in his book 'Turbulence', on page 122 - 124, section 4.1.4. It's stated that it still works because...

Homework Statement To research the physics of how a hot air balloon works. Homework EquationsThe Attempt at a Solution I just would like someone to check the main points I am going to include. The air inside the balloon is less dense because it is heated so that particles of air are further...

Are there any books that go into detail on how research in the physical sciences works? For example, analyzing whether a hypothesis is falsifiable or not. I want to be a physicist, and I want to know how science is done right in order that I can be a good physicist/scientist. Thank you.

Moved this question from the quantum physics section to this section, since... Well it fits this section better since electrons apparently do obey conservation of momentum in the 'classical' sense. Why not produce thrust in microgravity with electrons? Plenty of harnessable electricity in...

So everyone says that your should eat 5x a day. I've done that for years believing it's a healthy habit. But I was always hungry and couldn't lose weight. Now I've started eating 3 times a day, larger meals of 500-600 calories mostly based on fat and protein and I feel great! I have no need to...

Hello! (Wave) The nodes $A,B,C,D,E,F,G,H,I$ are given and are related as follows: The nodes $B,C,D,E,F,G,H,I$ are tasks that are done so that a work is completed , for example a building, and the cost $p(a,b)$ are the days that are needed so that the work $b$ finishes if the work $a$ has...

First of all, I am not from English-using country so excuse my short english skill. This is the question from Halliday. I have solved this problem and checked the answer from my reference which started its statement with below F + Fn − (m + M)g = (m + M)a where m = 0.250 kg is the mass of the...

The well-known eigen value expression A(a)=a(a) assuming the operator which represents a physical phenomena acts on a quantum state which is represented by an eigen vector, (a) corresponds to an observed value a. But I am wondering if the same operator A can act on (a) and produce another eigen...

Through some of the conservation of energy problems we've been working recently with the loop the loop (ball rolls down ramp and around a circular track.) there is one concept that is irritating me. This is not a homework problem but a mash up of the driving concepts from a few different...

If I plug my electrical device in the socket in any direction the device works. If i plug the device in opposite direction, it makes no problem. while the current in the socket is coming in hot wire. Is there hot and neutral also in the wire connected to the device or they are both hot ?

This just out of curiosity because the system works either way, I just wonder why. I have a high precision GPS system, there are two antennas placed about 2 meters apart with cables that are about 8 meters long going back to an embedded computer. Besides giving you the position, it uses the...

Question outline: In the case of 5d Kaluza (Klein) GR with NO charge and NO gauge field we expect 5d to reduce to 4d GR exactly. So this should be a very simple useful sanity check.s the side and corner terms of Einstein, Ricci and Energy tensors are zero, then R would be the same in 4d or 5d...

Hi, I have recently been using Apache for a web server. I would like to know more about how it works on a low level, what exactly it does. Perhaps a pseudocode, or minimal code version exists somewhere?

Hi everyone. A door closer is that thing above your office door that makes it close on it's own, but not super fast. It's basically a piston to slow it down and spring to pull it shut. It has two arms, one hinged to the middle, horizontally speaking, of the top of the door. The other...

1: Faraday's law states that a changing magnetic flux induces a voltage. 2: Voltage is the integral of E field with distance. 3: In a superconductor, or equivalently an with idealized wires having 0 resistance, there can't be any electric field inside. Thus, voltage in a superconductor should...

To make a hologram a film is exposed to an incident plane wave and wave from the object to record the interference pattern on the film. The principle is commonly explained in a way like that in p.1212 of "University Physics" (...

Hello I'm new here at Physics Forums and have been struggling with understanding how a simple pyrotechnics works, and thought I'd try you guys. As i understand pyrotechnics heat up, making them very hard to control and dangerous to people around them but is the extreme heat really...

I can't understand how eye actually works. From what I understand when I look at 2 objects of the same size The object that is further is smaller in the final image because light rays reflected from it take smaller surface at the retina (Here B is smaller than A because rays take less surface at...