Explanation Definition and 982 Threads

In the part below where the author of this solution, wants to show that: ##a\vee (b\wedge c)=(a\vee b)\wedge (a\vee c)##, in the third equality he adds ##2ac+2ab+2abc=2a\wedge(b\vee c)##; can someone explain to me why can we do this here? Thanks!

Could someone please explain to me why all my posts have disappeared from the Cosmological Redshift in Simulated Universe thread?

This is my answer to the ODE (I think it's correct) via Laplace transform, but I'm more concerned about whether or not my explanation for part b is correct or not? Any help would be greatly appreciated!!

I know that any number (except for zero), any variable and any term raised to the zero power is 1. I don't know the reason why this is true. Can someone explain why? Samples: 59^0 = 1 R^0 = 1 (a + b)^0 = 1

Not sure this is the correct forum; if a different forum would be more appropriate please advise: where is there a complete explanation of a magneto starting from the Physical Magnet's AC current thru to the Secondary Winding output. Some of aviation is totally dependent on a magneto and it...

https://www.feynmanlectures.caltech.edu/I_09.html

For this problem, The solution is, However, does someone please know why we allowed to assume that the derivative exists for f i.e ##f'(a) = \lim_{x \to a} \frac{f(x) - f(a)}{x - a}##? Thanks!

I have read lots but still, there're some really unproductive explanations of dirac delta function. So hopefully, you can explain it by following my arguments and not formal definition because I've read it all. It's shown to be as ##\delta (x) = 0## when ##x \neq 0## and ##\delta (x) =...

I thought of this description recently and I think it's pretty intuitive, but I've gotten some side eye telling it to friends and family (maybe because relativity is screwy, maybe because I'm confused, maybe both?) so I want to get some confirmation that it's reasonable. Here goes: If you're in...

My textbook introduces this angle concept really early on and I still don't understand it. It just shows that a normal to a line and some other random angle shown is the same. I don't see any transversal angles or anything. Where did they get the secondary line to form theta for the normal line?

Hello, I'm looking over some old school notes and re-learning some basic heat transfer. I have known Fourier's Law (1D: ##q = k\frac{dT}{dx}##) for a long time, but when I look at it now I find it strange that heat flux is inversely proportional to the length of the conductor. I would think...

So I've been trying really hard to understand the theory of relativity at its most basic level lately, and recently I dove down the rabbit hole of the Twin Paradox. This has led me through a series of youtube videos, each one claiming to present a different solution, explain why the other...

I'm studying Differential Equations from Tenenbaum's, and currently going through non-homogeneous second order linear differential equations with constant coefficients. Method of Undetermined Coefficients is the concerned topic here. I will put forth my doubt through an example. Let's say we are...

Dear collegues, I would like to share and discuss a simple explanation to the matter-antimatter asymmetry. Maybe this explanation is too simple, but your feedback is appreciated. I would like to start with what inspired me to this idea. The Hawking radiation. You know the event horizon of a...

https://physics.aps.org/articles/v15/162 Looking for a layman's summary of this article. If I spent a couple of hours maybe I could do it. Then again, maybe not.

I was reading a thread on my phone that was reviewing a paper about DM being explainable by gravitomagnetic effects. Now I can't find it in any search. It was on its fourth page - so at least 80 posts over at least two years. Anyway, what I wanted to ask was for a description that a layperson...

Planning a kitchen renovation. We've found a SIEMENS iQ700 glass downdraft extractor [model LD98WMM60B] that we'd love to use. It, of course, is only available in EUROPE. EAN code : 4242003907122 Connection rating : 300 W Fuse protection : 10 A Voltage : 220-240 V Frequency : 50; 60 Hz Plug...

In Chapter 3 of Thomas’s Calculus, they give the following proof of the Chain Rule. After the proof, the text says that this proof doesn’t apply when the function g(x) oscillates rapidly near the origin and therefore leads delta u to be 0 even when delta x is not equal to 0. Doesn’t this proof...

From my reading of several quantum optics textbooks and spectroscopy texbooks, the emission and absorption spectrum of an atom or molecule are always given in terms of the time-correlation function, for example the emission spectrum of a two level atom is given by: $$...

How did you find PF?: a web search on an item I am fact-checking. I have very little background in physics specifically. I do have a thirst for knowledge. I seek treasures in many places, when I find one I attempt to correlate and ingrate it with other tidbits I have found. I have more of a...

Would anyone know of a book or article that comprehensively explains Natural Units? I am looking for a document that explains all the versions of natural units and why, when, and how to use these units. I am looking for a source that provides many examples of how to use Natural Units. I found...

Good afternoon. I have some questions about the details of epsilon-delta proofs. Below is a simple, non-linear limit proof example which will serve as an example of the questions I have. The questions are below the example and involve clarification and explanations of steps and details in the...

Hey! :giggle: I found online the following code for a christmas tree in Python : tree_height = input("Enter the tree height : ") tree_height = int(tree_height) spaces = tree_height-1 hashes = 1 stump_spaces = tree_height-1 while tree_height != 0 : for i in range(spaces)...

I am new here, so pardon my ignorance. First of all, I am aware of the impossibility to distinguish experimentally between SR (Special Relativity) and LET (Lorentz Ether Theory). I know there is a PF policy article on LET and the Block Universe. I must admit though that LET is more appealing...

What is the physical explanation behind the pedrail wheel (a.k.a the walking wheel). Someone said it "makes it's own road", but how does it allow a vehicle to climb stairs, navigate rough terrain etc.? I have looked all over the Internet and even visited a university library, but information on...

In one book on quantum mechanics, I found a very simple analogy to Bell's inequalities, which explains their essence without delving into the details of the physical experiment. I liked this analogy, but it seems the authors got it a little confused, so I ask for clarification if it is correct...

Does anyone know if the Gage Block physics is now understood?

I am familiar with Cantor's work on the concept of infinity and his use of the set theory to explain various types of infinities. Having said that my intuition never seems truly grasp/accept it. Is there a way to train my mind to see this seemingly contradictory situation as a fact? This is...

A simulation/animation/explanation based on the inertial frame only: The previous videos referenced there are here: See also this post for context on the Veritasium video: https://mathoverflow.net/a/82020 Note to mods: The previous thread is not open anymore so I opened a new one. Feel free...

when I had learned matlab, my professor told me a website where everything is explained about MATLAB variable and MATLAB function. After a long time later, I like to use MATLAB for my work. However, I forget the name of the website. Does anybody tell me the helpful website?

Understanding R0 Since it seems that most members visit General Discussion, probably this is a good place to post a topic like this, since everyone uses the term. And it would be nice to understand it. A guide from Nature.com meant for more general reading public...

Explanation 1: Eddy currents induced, energy loss due to joule heating. Explanation 2: Eddy currents induced, induced magnetic dipole formed. Energy is lost as work has to be done to overcome the attractive/repulsive force due to the magnet and the induced magnetic dipole from the eddy...

I am not sure if this is the correct place to post so I am very sorry if I am posting in the wrong place. I am looking to have the four fundamental forces of physics explained as simply as possible, I have been doing some online research to try to understand it and I am having a hard time...

To an average person with high school math knowledge how would you explain in a few words why no object could travel faster than the speed of light ? Well it's because...

OK, I have read all the Fanno flow equations, I understand mass and enthalpy conservation for adiabatic flows give the result that friction causes Mach number go to 1... But I cannot think of a physical explanation for the counter-intuitive fact that friction both accelerates and cools the...

When a magnet moves near a non-magnetic conductor such as copper and aluminium, it experiences a dissipative force called magnetic braking force. I am rather confused by the following explanation of magnetic braking force: The non-magnetic conductor here is the aluminium 'wall' seen on the...

This is a very simple question. I've read a fair bit about the greenhouse effect and how GHGs affect the Earth's surface temperature and I know it can get very complex. But if I boil it down, it seems to be a very simple thing. Am I right to think of it this way? Radiation from the sun reaches...

D is correct, the reasoning is as follows: 1/2*(M1V1)^2 + 1/2*(M2V2)^2 = 1/2 * (M1 + M2) (Vcm)^2, since V1 =V2 =Vcm KE retained = KE final = 1/2 *M(Vcm)^2 Let me know if reasoning is okay? However, why A isn't correct?

For this question the ball is rolling without slipping so that means the velocity of the point of contact is zero. Does that also apply to the acceleration of the point of contact? Because that’s what I assumed and I applied the relative acceleration formula above and use the starting point to...

This video explains gravity in a way I haven't encountered before (regardless of how irritating the presenter may be). Nevertheless, I find it hard to believe that a squirrel falls from a tree to the ground due to gravitational time dilation between its head and its feet. The amount is so...

If I have an NPN transistor and let's say we set the base voltage higher than the collector voltage.(Emitter is connected to GND).There are 2 currents flowing in the base because we have two forward biased junctions inside the diode , 1 is the current flowing from emitter to base and 1 is the...

Take a medium with ##n = n(y)## and define the functional as usual$$T[y] = \int_{\mathcal{C}} \frac{ds}{cn^{-1}} = \frac{1}{c} \int_{x_1}^{x_2} dx \, n(y)\sqrt{1+ y'^2}$$along ##\mathcal{C}## between ##\mathcal{P}_1 \overset{.}{=} (x_1, y_1)## and ##\mathcal{P}_2 \overset{.}{=} (x_2, y_2)##...

What is the classical explanation for why the microwaves won't pass through the microwave door?

Thx !

Hello good people! I'm studying the compressible flow and the book refers to this example. I can't understand how does it calculate the angle Θu? In the previous example, there is a method to calculate it but it requires all the properties once the fluid is deflected, therefore, that's not the...

So far, I found the derivative of ##f##: \begin{align*} \frac{d}{dx}\,f(x)&=&-\frac{d}{dx}\,\ln(-x)\\ &=&-\left(\frac{1}{(-x)}\right)(-1)\\ &=&-\frac{1}{x} \end{align*} ##f'(x)## is always positive and never zero on its domain. Hence, ##f## does not have a local maximum and is always...

Links for some of the science are included - this presentation is based on press releases. The peer reviewed data will be available shortly. Some things to note - results show both 64% and 90% effective,the video explains this one The tests looked for positive Covid tests in volunteers...

I'm looking for a source that fully derives the complete formula for the surface area of a general (triaxial) ellipsoid. I'd prefer a source that has more than just a full derivation, but also has a fair amount of prose discussion on this topic. Some historical context would be nice, as well...

The spectrochemical series of metals, under the circumstances that same ligands are used and that it is in an octahedral coordination, is given by: Mn2+ < Ni2+ < Co2+ < Fe2+ < V2+ < Fe3+ < V3+ < Co3+ < Mn4+ < Mo3+ < Rh3+ < Ru3+ < Pd4+ < Ir3+ < Pt4+ When I was skimming through a textbook to...

Is the presenter's explanation correct in all respects? And has anyone seen one of these "in person"?