Explanation Definition and 961 Threads

Hello all. In his books on classical mechanics, David Morin claims that when computing the work W = F Δx done by a contact force that don’t involve any slipping, we can equivalently say that Δx is the displacement of the thing that is applying the force. Later, when analysing a wheel rolling...

Is there a simple explanation for fermi-dirac statistics? I can't understand how a particle can "follow" a statistic.

Homework Statement Homework Equations Work Done=Force*Displacement in the direction of the force The Attempt at a Solution I tried to solve the problem this way, I wrote these equations for the two masses, T-mg=ma...(i) Mg-T=Ma...(ii) From (i)&(ii), T=[M(g-a)+m(a+g)]/2 and then I would...

So I have a question regarding the Alcubierre metric and the phenomena of stars on outer edges of galaxies moving at higher velocities than their orbital calculations state they should. When taking the accelerating expansion of space into account due to dark energy, could a sub-luminal...

Hello, Recently, a solar power tower plant was founded next to where I work. Since it's the tallest object in the area, it's quite hard to miss it. But apart from that, every morning the reflected light is arranged in a hyperbolic- like way, as you can see in the picture. Does anyone have a...

I am reading Kaplansky's text on metric spaces and this part seems redundant to me. It was stated below (purple highlight) that we need to show that the convergence of ##(f(a_n))## to ##c## is independent of what sequence ##(a_n)## converges to ##b##, when trying to prove the claim ##f(b)=c##...

Hi everyone, I came upon a simple mathematical conundrum a few decades ago that has irked me for a while now and for which I don't have a reasonable mathematical explanation. The only reasonable "explanation" I currently have is that 'certain mysterious things happen when tending towards...

Ok so these are two different goals. But mathematically, I don't see how one can explain well without also being able to predict well. After all, regression is about function estimation regardless of which goal. If we can infer well using the coefficients, then we should be able to predict well...

Many sources give explanations of the Riemann tensor that involve parallel transporting a vector around a loop and finding its deviation when it returns. They then show that this same tensor can be derived by taking the commutator of second covariant derivatives. Is there a way to understand why...

http://oeis.org/A000088 This is a list that gives the number of simple graphs on n unlabeled vertices. Could someone conversant in graph theory explain why the number of simple graphs on 4 unlabeled vertices, which is 11, is the only one that seems to be odd (nontrivially), while the rest seem...

Can Stimulated Emission in lasers be explained semi classically? If so, how?

I apologize if this is not the correct forum for this thread. I have tried to find a discussion regarding this question on the Internet without any success. The Wikipedia discussion https://en.wikipedia.org/wiki/Baryon_asymmetry makes no mention of any statistical explanation, so I understand...

Homework Statement What would have caused humans to come up with fractional exponent notations? Homework EquationsThe Attempt at a Solution I understand that it makes sense to use the exponent notation when we have to multiply the same number a number of times. For example, 10^8 is the short...

Hi there guys, I was wondering does anyone have a layman's explanation of the GCRS as defined in the title. I am confused as to whether this is an inertial or non inertial system. In text modern reference books such as this (chapter 10, section 10.3.2) they define rotating/non rotating...

I'm curious if the readers of this astronomy forum, at this point, have come to understand that the mass-luminosity relation has little to do with the physics of nuclear burning. The reason I ask this is that it is, unfortunately, still common to find textbooks and course websites that say it...

Homework Statement In a practical that we conducted, we were investigating the relationship between Launch height and the range (horizontal distance it travels) of a projectile. We launched a projectile from various heights and measured the horizontal range it traveled before reaching the...

Homework Statement 1) Suppose ##t## is a subsequential limit for ##(s_n)##. Write the precise definition of the meaning of this statement. 2) Explain why there exists a strictly increasing sequence ##(n_k)^\infty_{k=1}## of natural numbers such that ##\lim s_{n_k}=t##. Homework EquationsThe...

Hello, I am 12 years old in 6th grade and love physics and Quantum Physics, I would love an explanation of Quantum Physics and Topological Quantum Matter.

In his second lecture of the QED series (see below), Prof. Richard Feynman explains the phenomenon of reflection from a plane mirror, and then the working of a diffraction grating with his theory of arrows (probability amplitudes), and we see that how the new theory, which is much moved from the...

Students seeking “deeper” understanding of basic electricity, frequently come with one of the following misconceptions. 1. Electrons are like balls, they start with potential energy and gain kinetic energy. They deliver their energy to the far end of the wire by filling a bucket. 2...

For many years, the measurements of the Landé g-factor of the muon have been puzzling, as the experimental value and the theoretical predictions showed some disagreement - 3.6 standard deviations for the last years. Experimental and theoretical uncertainties have a similar size, so work on both...

Homework Statement I have no idea what torque of a friction in a bearing is. I'm looking for good explanation. Homework EquationsThe Attempt at a Solution I understand what torque/friction/bearing is. But I have no idea how they come together when looking at the actual mechanical problem. Help!

Hi I have found a YT video in which there is an object recorded on infra red camera. It makes very strange maneouver. Is there any explanation what this could be? Thank you ( I have edited video so it shows only interesting moment).

In the first volume of his lectures' books, Feynman tries to mathematically describe that in a particular gas ( particular because in this case is the sum of 2 monoatomic gasses with different masses) as a result of the collisions beetween atoms it will be equally likely to find any pair moving...

Hi the question is about bicycle and motorcycle dynamics How can we explain the motorcycle leaning in turn without using the centrifugal force term? You know the correct term for rotational motion is the centripetal force and it is toward the centre. I have a problem with rotational equilibrium...

Hi, This YouTube video shows various shapes of pyrolytic graphite suspended on an alternating polarity matrix of square neodymium magnets. As I understand the principle of diamagnetic anisotropy, the stronger the external magnetic force, the stronger the induced repulsive force in the...

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!

Homework Statement The picture below. Homework Equations cos2x=1-2sinx sin2x= 2sinxcosxThe Attempt at a Solution I got the modulus by using the Pythagoras theorem which is 2sin theta But I faced difficulty to find the argument. I have no idea why i end up with tan a (alpha) = cot theta which...

When a test charge stands next to a wire, there are coulomb forces between the test charge and the protons of the wire. 1: When the test charge starts to move, the Coulomb forces stays the same, because distances from test charge to protons stay the same. There is no magnetism in this case...

Hey all! I am prepping myself for a quantum course next semester at the graduate level. I am currently reading through the Cohen-Tannoudji Quantum Mechanics textbook. I have reached a section on the density operator and am confused about the general concept of the operator. My confusion stems...

A card kept on a glass with a penny is jerked. The coin falls in the glass while the card moves away. why is that? My attempt at an explanation A force acts on the card which is greater than the static friction acting between the card and the coin. Hence the coin is able to overcome that...

Homework Statement Plotted a distance vs time graph for acceleration on an inclined plane (constant acceleration) and got graph equation of y = 10.242x^2 + 25.996x - 10.315 So this means that d = 1/2at^2 + vt - y intercept Meaning 1/2 acceleration is 10.242 and initial velocity is 25.996...

Please could someone explain, pretty simply, what a parameter and also its relation to graphs? And if possible give a couple of examples. I have trawled through the internet and can't find anything which I understand. Thank you very much.

I don't uderstand how, using special relativity theory (time dilatation and length contraction), one can explain why in the Michelson interferometer there is no delay between the two rays in the reference frame where the interferometer is moving. Consider the picture ##2.## Setting...

Background and Motivation In the Standard Model, a muon is simply an electron with a bigger mass. But, measurements of the radius of muonic hydrogen and the muon magnetic dipole moment (muon g-2), show a fairly significant discrepancy between theory an experiment in that respect, at the five...

Homework Statement Please provide a physics explanation of this question: How does load current affect the potential difference across the terminals of a cell? Homework EquationsThe Attempt at a Solution p.d. inversely proportional to current. Thus, when I increase, the p.d. decrease and vice...

Hi. I'm going over the discontinuity aspects of the electric field as we cross the surface charge. A pillbox Gaussian surface was drawn and the electric field for "below" is throwing me off. Can someone explain why the electric field is pointing in the same direction from both sides of the...

I just saw this news article on the home page of the university I'm working in: http://www.aalto.fi/en/current/news/2017-06-30/ It seems to be about a study that can potentially explain the redshift of distant stars with a mechanism that's related to the interaction of photons with the...

Could someone explain to me how a Siphon works using Bernoulli's equation. Why would one beaker have to have a higher height than the other beaker? My thoughts were that a Pressure differential is needed for water to flow, so the input and the output pressures must be different. In...

Hi, I saw this video and I can't explain why the magnet is propelled to the end of the coil with such a huge force. Can someone explain it in clear terms. I also tried to use Flemings left hand (or right hand) rule but it did not give me a satisfactory answer. Thanks, SM

Hello everyone, The questions I am about to ask have probably been explained already, but even after everything I've read I still cannot understand how this experiment would play out and how to answer these questions. So without further ado here is the experiment: Imagine you have person A...

So I just began a course on Linear Algebra, and was curious about how we can estimate derivatives using centered differences: After a few minutes of Research, I find the proof involving something about a truncation error, which led me to the conclusion that when estimating derivatives, the rate...

I am looking at this brief derivation of the E cross B drift for a plasma, starting at the top of page 3: http://www.physics.sfsu.edu/~lea/courses/grad/motion.PDF. I am a bit confused as to the justification that the drift velocity is perpendicular to the magnetic field, as stated at the top of...

I am doing a review for a Dynamics exam, but I am having trouble with this one question (below). Please note the top of the picture contains the answers. What I have done is make a free body diagram that includes the tension of the cable and the weight of the rider/swing. So according to my...

Hello! I hope this is the proper forum for my question(s). English is not my native language, so I apologize in advance for language mistakes. In Feynman Lectures on Physics, there is a chapter about the conservation of energy. The first part, which deals with the definition of energy, I...

Homework Statement Why integration of $$\frac{D^2\mathbf r}{Dt^2}=−2\mathbf w \times \frac{D\mathbf r}{Dt}−g\mathbf R$$ gives us $$\frac{D\mathbf r}{Dt}= \mathbf v_0 −2\mathbf w×(\mathbf r−\mathbf r_0)−gt\mathbf R$$ Homework Equations Consider a time-varying vector written in the body...

In 1727, astronomer J. Bradley discovered the phenomenon of stellar aberration. All stars throughout the year on the celestial sphere pass ellipses with an semimajor axis observed from the Earth at an angle of 20.5. Aberration is caused by the movement of the Earth in its orbit around the sun at...

<Moderators note. Moved from the quoted thread to avoid detracting> Newton third law does apply in magnetism, and this is proved by applying the conservation of momentum principle. This will be clearer when the causes/origin of the magnetic force is understood as described in the work "Two new...

Homework Statement I need to research Hess' law, but I can't find a simple explanation. I know that the enthalpy change between the reactants and products is the same as the enthalpy change between the reactants and something else, and between that something else and the products, but I don't...