Physical Definition and 1000 Threads

Reason I posted this in the maths help forum is that an equation of this form randomly popped up in a homework I was doing on differential geometry. I started with a one-form ω=dβ (β is a scalar function) and found that if for a random vector v, ω(v) = 0, then \frac{d}{dt} \left(...

Homework Statement This isn't strictly a homework question as I've already graduated and now work as a web developer. However, I'm attempting to recover my ability to do physics (it's been a few months now) by working my way through the problems in Analytical Mechanics (Hand and Finch) in my...

i.e. "A F = <0,0,10> is exerted at the point (1,1,1) what is the moment about the X axis?" i know the answer is <sqrt(3),sqrt(3),sqrt(3),> DOT (<1,1,1>x<0,0,10>) but the physical meaning of that escapes me. in what applications would an axis be more useful than a point? thanks!

How many meters will light travel in 83.8 hours? what I came up with is (3x10 m/s) (83.8hr) = 2.5 14 x 10 answer 2.5 14x10 m teacher marked it wrong very confused.

Physical laws ... are they material?! There was an old question about physical laws , where do they come from? as they are considered separated from the material of the universe. Of course I know that they are produced by the human brain or human consciousness (which is material in turn) , but...

Hello PF! (Not sure this is in the right section.) I've learned very little about maths/physics in school, but went back to uni last year to do maths. Physics is still a bit of an alien territory, but nevertheless I like exploring it in my own amateur way. One of the things that started...

As far as I have seen, all physical models begin with space, and then put matter that live in space and modify it somehow. Basically the models works fine and describe reality farily well. But at some point they arrive to problems, as infinite curvatures, that prevents them to be unified. It...

Hello experts (or even the not so experts) in QFT. Have you encountered before the following stuff on QFT? http://www.scribd.com/doc/58635278/Introduction-to-a-Realistic-Quantum-Physics The following is an example of what it's saying: The basic idea is that: Please find critical...

I was wondering what were the fundamental physical units of measurement, ie those from which all other units can be derived. To my mind, there are only two things which exist in the universe and from which all units of measurement can be derived : space and matter. The reasoning is as follows ...

How does a CPU send information to memory locations - physically? I know in software you can reference memory locations. I'd like to know how a CPU references them? I understand that it symbolizes a memory location using bits (00000101 = 5) but - how does that string of bits work in the...

In some class notes I found those conditions interpreted as a "five requirements on Hamiltonian of physical system": 1. Unitarity -> Hamiltonian has to be hermitian operator 2. Claster decomposition (microcausality and locality) -> (? missing part) 3. Poincare invariance -> Hamiltonian...

Out of many properties polymer scientists are interested to calculate one of the most common is "Rg" i.e. Radius of Gyration. Can anyone put more light on the physical significance of this value? Can Rg value of two polymers be compared? If yes what conclusion can be drawn from such comparison?

How can I see that the generators of the Galilean group correspond to energy, momentum, etc.? References which cover the Galilean group and algebra as well as their realization in phase space are appreciated, especially if they are not too sophisticated. Thanks kith

Is there anything in the physical world that is actually random even after we were given every single bit of information needed to calculate an outcome? Rolling a die or flipping a coin doesn't count, because if we did all the calculations, we would be able to calculate what the outcome would...

I wonder what really happens to powers in capacitors and inductors when they are connected in a circuit either in series or in parallel. I know that inductors have a positive reactive power while capacitors a negative one, so I imagine inductors release energy while capacitors absorb it, but it...

Thanks to the American Physical Society for my New Calendar! Not only is the calendar nice, but the envelope it came in is just the right size for me to work out all my new equations without having to spring for an easel-size paper tablet or a chalkboard! (I'm a little on the cheap side!)...

I've always found it pretty amazing that human beings can understand the rules that govern the universe we live in, but is there a fundamental reason as to why they are comprehensible at all? Do they have to be rooted in logic? If it's just something that is unknown, that's a perfectly...

If a sugar cube size piece of neutron star weighs as much as every vehicle in U.S.A, and H2 in the core of Jupiter has been compressed to a metalic version of itself, what then is the limit of compression? Can matter be compressed further than that of a neutron star?

Could we harness energy from Earth movement relative to physical vacuum? Earth is moving around Sun with speed of 30 km/sec. Also there exist force of Casimir and similar effects. If we have some body (for example a ball) which is moving in some media (for example water) then to harness...

Hi I was just wondering what ways you can smash glass without physically touching/breaking/throwing something at it. For example, I know that the "force" of an explosion can break glass that is a fair distance away from the actual explosion. So is there any way you could make something that...

Hello, Given the hamiltonian : H = -( aS_z^2 + b(S_+^2 +S_-^2) ) with S=1 and a,b>0 are constants. working with the base: { |m=1> , |m=-1> , |m=0> } The matrix form of H is: H = \left( \begin{array}{ccc} -ah^2 & -bh^2 & 0 \\ -bh^2 & -ah^2 & 0 \\ 0 & 0 & 0 \end{array}...

Hi all, I'm trying to understand exactly what the physical meaning of conductivity/current is in relation to waves. if we have a wave traveling through a conductor, we find that it decays exponentially, i.e. e^{-\alpha z} where \alpha=imag(k)=\omega\sqrt{\frac{\epsilon\mu}{2}}...

By "physical particle" I mean color-singlet particles which have asymptotic T=\pm \infty states. How many stable particles exist in the theory? Only one? SU(2), SU(3), and SU(N) gauge groups can all be discussed.

I have seen PeterDonis state that predictions of GR are expressed as contracted tensors i.e. scalars. And they are coordinate independent. So I have a question what these scalars represent physically? Could it be that they represent measurements of physical quantities (with tensors dual...

I try to get the gist of the Special and General theories of relativity for more than two years now. And I still don't understand if the geometrical explanation really explains or just describes what is physically going on when talking about all the relativistic effects (like gravitation, time...

Hi guys. Sorry if this is in the wrong topic, but what is the physical size of an electron? I understand it can sometimes behave as a wave. But when it is a particle, just how big small is that particle?

Does anyone know what the physical property measured in seismic surveys is? Seismic surveys used in searching for hydrocarbons to be more specific. I was thinking it would be the rocks density but I'm not sure, can anyone help please? :)

Homework Statement The physical pendulum shown on your paper is a 27.0 kg wedge of a circular disk of uniform density with radius, R=1.87 m and opening angle β=0.847 radians. The pivot point of the pendulum can be moved along the center line of the wedge as shown on your paper...

Homework Statement The Clausius-Clapyeron equation ln(p2/p1) = -ΔHvap/R (1/t2 - 1/t1) is derived assuming that ΔHvap is independent of temperature. Find ΔHvap as a function of temperature for ethanol at constant external pressure.Homework Equations these are not relevant equations but the...

Dear friends In quantum mechanics what is the physical significance of normalizing a wave function? Thanks in well advance

Go easy, not an expert. My intuition tells me that the maximum possible entropy in a given space is going to coincide with the arrangement requiring the most information to describe it. Let me know if this is wrong. Ok, so now what I want to know is what an actual arrangement like this...

Hello. I'm trying to understand why, in terms of Maxwell's Equations, the ratio of the number of turns in a transformer converts an input voltage to an output voltage. EE explanations only seem to go as deep as this article: http://en.wikipedia.org/wiki/Transformer#Basic_principles They state...

I can now although do the maths related to plane stress etc but I have struggled to grasp the logic behind this concept. It says changing the way you see the stress by rotating the view, stress changes. My question is why ? Why is this so that we see stress with one value when standing at let's...

Thought experiment: Say for instance that a Baseball game is being played out on a planet that is orbiting the outer edge of a black hole. You, from deep in space away from any gravitational source, are watching this game from a powerful telescope. The batter comes up to bat; the pitcher...

If ρ is the desity operator of a ensemble. We get (ih/2π) ∂ρ/∂ t = [H,ρ ]. for a stationary state [H,ρ ]=0 . So H and ρ can share the same eigenvectors. Can someone explain what does this mean? :smile:

I understand the basics of the mathematical descriptions of systems in superposition. But what I'm not clear about is whether such a system is actually in more than one state at the same time. Is this a matter of QM interpretation or is it simply moot b/c we can make no measurements that can...

I'm currently enrolled in precalculus and I'm finding that almost everything we've learned so far is just Algebra 2 review. I've been looking for a book where I can self study Calculus and move ahead, and I stumbled upon Calculus: an intuitive and physical approach by Morris Kline. I am...

Homework Statement Estimate ΔG for the process where one mol of ideal gas is subjected to an increase in pressure from 1.00 atm to 11.0 atm at 25.0°C. Homework Equations ΔG=ΔH-TΔS ΔH=C(p,m)(Tf-Ti The Attempt at a Solution Seems straight forward, but it seems i am not given...

Hi, I'm trying to simulate the ship traveling in ice. Basically, I would like to assume that the rigid body dynamics is sufficient to do the job since the main point here is the interactions between rigid ice fragments and the rigid ship. The fluid interactions with ice fragments should be...

Sorry for the confusing title! I have a question that I cannot wrap my mind around... Suppose the universe attains its state of maximum entopy (assuming maximum here also involves quantum effects such that in the end even the atoms disintegrate into photons and leptons). I understand that in...

The Feynman slash \slashed{a}=\gamma^\mu a_\mu maps a four-vector a to its Clifford algebra-representation. This is a linear combination of the gamma matrices with the components of a acting as expansion coefficients. What physical significance does this new object have? The gamma...

A phase factor is e^{i\phi}. Mathematically a multiplication of a wavefunction by phase factor is equivalent to a rotation of the state vector by the angle \phi, however the probability amplitudes are unchanged. So what is the physical meaning of it?

Hello, I am a chemist and have been working on chemical dynamics. Recently I have started working on some many body interactions. Therein I have found some ideas about Fock Space, Fock Matrix, Fock Space Coherences. These are extensively used to provide characteristic information in...

I googled this and surprisingly no one seems to have an answer. What would have to be done to the water to make it change chemically?

I'm currently applying for various graduate schools in both physical chemistry and condensed matter physics. My undergraduate degree is a double major in both fields. I'm curious about what the differences between the departments (and, to an extent, fields) might be. In terms of research...

I'm not sure if this belongs here or in the physics section. The mathematical definition of curvature is the derivative of the unit tangent vector normalized to the arc length: \kappa = \frac{dT}{ds}. If we apply this to a parabola with equation y = x^{2} we get \frac{2}{(1+4x^{2})^{3/2}}...

I am using ifftshift function in matlab, mathematically it does the following functions If M is a row matrix: M = 1 2 3 4 5 6 7 8; then ifftshift(M) = 5 6 7 8 1 2 3 4, i.e. it replaces first half with the second half. Although how can be explain this function physically?

Homework Statement A physical pendulum is made of a uniform disk of mass M and radius R suspended from a rod of negligible mass. The distance from the pivot to the center of the disk is l. What value of l makes the period a minimum? Homework Equations The Attempt at a Solution

Hi, I some basic questions on the physical meaning of bra-ket notation. I have looked at a lot of material, and I have seen descriptions of the algebraic properties of bra-kets, and I have seen hints at it having meaning regarding the probability of events happening/state changes, but I can't...

I've been looking at the various Planck units, and I'm wondering how they are constructed from the constants involved. Like is there any physical reasoning behind those equations? I've looked all over the place for derivations of the equations or what the actual physical meaning of the units...