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Force, constant velocity, and 0 velocity

When a body has a net force of 0 on it, one cannot say that it is at rest or in motion at a constant velocity. If a body is accelerating because of some force and I want to stop it, I can apply the ...
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What is the 'super' parameter of superconductivity and what is the role of Cooper pair?

Only thing I know about superconductors is that here the electrical current face zero resistance. My first question is what is 'super' (physical or mathematical entity) about a superconductor. Or more ...
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How did Newton discover his third law of motion?

How did Newton discover his third law? Was it his original finding or was it a restatement of someone else's, like the first law coming from Galileo? What initiated the concept of what is now known as ...
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Streamlines tangent to velocity vector

As from the title, I'm not too sure how they are related. Definition is that streamlines are instantaneously tangential to the velocity vector of the field. Why would a streamline that shows direction ...
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LC Oscillator and relativity

There are two identical LC oscillators with electronic counters attached indicating how many times they have oscillated (from the time they are turned on). They are turned on simultaneously and one is ...
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Variance in speed of light

While discussing this question (Does light have an unending journey?) I stumbled on the fact that light's speed is constant only in inertial frame. What I happened to do was add up the expansion of ...
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Hyperkahler manifolds and their use in theoretical physics

Just as the title says: What is the easiest definition of a Hyperkahler Manifold? Could you give some examples of Hyperkahler manifolds, and manifolds which fail to be hyperkahler? Why are such ...
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Normal force and reaction

It is said that the normal force comes into play any time two bodies are in direct contact with one another, and always acts perpendicular to the body that applies the force. This force is a ...
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Conserved topological charge for d=3 Yang-Mills. G=U(2)

Consider a pure Yang-Mills lagrangian density $$\mathcal{L}=-\frac{1}{4}F^{\mu\nu}_aF^a_{\mu\nu}$$ with gauge group $U(2)$. Take the generators for $U(2)$ to be $t_0$, $t_i \ i=1,...,3$ with ...
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Deriving an equation involving Killing vectors

I'm currently studying Carroll's GR book Spacetime & Geometry, and ran into some trouble understanding the text. When discussing Killing vectors, Carroll mentions that one can derive ...
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How to imagine the first few moments of an LR circuit?

For example, there's a very simple circuit which only contains on resistor. So according to Ohm's law, we have: $\mathrm{emf} = IR$ As we know when time $t = 0$, the current must be $I = 0$. However, ...
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I am asked to show that an new defined operator: $$U_{\beta} = \exp(\displaystyle\frac{i\beta L_z}{\hbar})$$ is unitary, where $$L_z = -i\hbar\,\,(x\displaystyle\frac{\partial}{\partial y} - y ... 1answer 885 views Problem involving 1st law of thermo and ideal gas law Problem: 1.0 \text{ kg} of air at pressure 10^6 \text{ Pa} and temperature 398 \text{ K} expands to a five times greater volume. The expansion occurs such that in every instance the added ... 1answer 2k views Definition of the complex wavenumber My syllabus of electromagnetism defines the complex wavenumber as:$$k = \omega\sqrt{\epsilon\mu}$$with \epsilon the complex permittivity and \mu the complex permeability. Thus \epsilon and ... 2answers 428 views Virtual photons as force mediators in QED - really? If the photon is the force vector for EM interactions, e.g. electrons, how does each electron 'know' where the other one is so that it can send it a photon? I've thought about this for a while. I ... 2answers 497 views Does light have an unending journey? When we shine a torch in a room its light travels to the back of the room. What happens to the light of a star ? I dont suppose we can say it continues to travel to the back of the universe as the ... 0answers 497 views Beta function from exact renormalization group equation I'm trying to calculate beta functions from exact (or functional) renormalization group equation (I mean Wilson-Polchinski RGE). I've got the equations but I don't know exactly how to use the ... 1answer 264 views Quadrupole potential generation in Paul traps I am currently getting familiar with the concept of the Paul trap and the underlying physical principles. I do understand what kind of potentials are needed to trap charged particles, e.g. for the 3D ... 3answers 1k views A question on Bernoulli's principle Which is more appropriate regarding Bernoulli's principle fast moving air causes low pressure or lower pressure causes fast moving air. 1answer 960 views Expression for kinetic energy of gas per molecule The average kinetic energy (KE) per molecule of a gas is \frac{3}{2}kT. While finding this we do$$ \text{ Average KE} =\frac{1}{2} M \frac{1}{N}\sum v^2=\frac{3}{2}kT$$But why do we not add ... 1answer 131 views Vector analysis query [closed] I cannot understand how and why those two expressions are coming (the ones I have highlighted). Please explain. 2answers 2k views Amateur moon laser ranging Questions first, then my rough estimations: 1) Is it possible to perform moon laser ranging with amateur motorized 114mm telescope? My calculations suggest that for 1mJ laser it should receive ~2 ... 4answers 688 views How to end up with Newtons in the calculation of the lift force In another StackExchange Physics question, @Rego had found the following equation to calculate the lift force generated by a simple rectangular blade.$$F = \omega^2 L^2 l\rho\sin^2\phi$$in ... 1answer 562 views Work done should be positive but coming out negative? \int\frac{GMm}{x^2}dx where x varies from \infty to r. Situation we are bringing a very small mass from infinity to a distance r in the gravitational field of Earth with constant ... 1answer 110 views Dark Energy Explanation Found [closed] It's my sincere request to this Physics forum that if i am wrong (which has the least possibility atleast from my side) just reply "wrong" so that i can move on futher. I know personal theories are ... 3answers 903 views Are matter waves transverse and can they be polarized? Are matter waves transverse and can they be polarized? What I know:I'm aware of the de Broglie matter waves hypothesis and de Broglie wavelength relation(at a very basic level as part of high school ... 1answer 7k views Does the phase difference between voltage and current in an LCR circuit exist throughout the circuit? I know that in an purely inductive circuit the current lags behind voltage by 90^o, in a purely capacitive circuit vice-versa and in an LCR circuit the current may lag or gain with respect to ... 1answer 1k views How does heat energy travel in space? How does the heat energy from the Sun reach us on the Earth? Since the kinetic energy of an atom is the amount of heat energy and there is no matter in space, how does heat from the Sun reach us? 1answer 103 views Determining the location of magnetic moments The magnetic moment of a closed current loop is$$\mathbf{m} = \frac{I}{2}\int\mathbf{r}\times d\mathbf{r}. Note that $\mathbf{m}$ is independent of any coordinate frame. How, then, does one ...
Suppose a point charge $q$ is located at $(x=0,y=0,z=d)$, and that along the $x$-$y$ plane is a infinite plate of potential $V = 0$. Then the method of images solves Laplace's equation for the ...