What is General: Definition and 1000 Discussions

A general officer is an officer of high rank in the armies, and in some nations' air forces, space forces, or marines.In some usages the term "general officer" refers to a rank above colonel.The term general is used in two ways: as the generic title for all grades of general officer and as a specific rank.
It originates in the 16th century, as a shortening of captain general, which rank was taken from Middle French capitaine général.
The adjective general had been affixed to officer designations since the late medieval period to indicate relative superiority or an extended jurisdiction.
Today, the title of general is known in some countries as a four-star rank. However, different countries use different systems of stars or other insignia for senior ranks. It has a NATO rank scale code of OF-9 and is the highest rank currently in use in a number of armies, air forces, and marine organizations.

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  1. A

    Mathematical prerequisites for general relativity

    What mathematical topics do I need to know to start studying general relativity? From which textbooks can I learn them? I don't currently know anything about differential geometry. I know calculus, linear algebra, mathematical methods of physics (the necessary topics for quantum mechanics) and...
  2. G

    B General Relativity: Action & Reaction in Gravitation

    Hi, In general relativity, gravitation is not anymore a Force but a deformation of space time. I would like to know what's becomes the 3 law of Newton for gravity that action equal reaction ? When a apple fall on the earth, does "the force" is exactly the same as the one applied on Earth ...
  3. T

    I Finding a general formula for a recursive sequence

    The general formula for the nth term of the Fibonacci sequence where an=an-1+an-2 can determined by matrix diagonalizations Is there a way to determine the formula of any recursive sequence say an=a1+a2+...an-1
  4. Jamestein Newton

    I Discussing General Relativity - Beliefs & Ideas

    Following are not strictly physics questions. But cool questions to discuss. We need to add dark energy to our cosmological model if we strictly follow GR. This lead to some beliefs that GR is an effective theory. (1)Do you believe that GR is the fundamental theory? If GR is an effective...
  5. rudransh verma

    B What is the focus and parameter of a parabola with vertex off the origin?

    The general eqn of parabola is ##(x-h)^2=-4a(y-k)##. This is the parabola whose vertex doesn't lie on origin and axis is parallel to y axis. It opens downwards. Vertex is (h,k). What will be the focus of this parabola and what is ##a## in general form? In the diagram a<0 which is...
  6. The Bill

    Applied Resources for general vector differential equations?

    I'd like a good set of notes or a textbook recommendation on how to approach vector differential equations. I'm looking for something that isn't specific to one type of application like E&M, fluid dynamics, etc., but draws heavily from those and other fields for examples. I'd strongly prefer a...
  7. Aerodyn

    I Understanding Gravity with GR: Beginner's Guide by Aerodyn

    Hi everybody. I recently started to learn GR from a very begginer level. I would like to share with you some lines of discussion, to understand your approach to some specific topics which for me are key to better understand the whole story. If a put an accelerometer on the floor it reads 9.8...
  8. Tertius

    I Computing Volume in General Relativity: Use of Tensor & Friedmann Eqns

    When we compute the stress energy momentum tensor ## T_{\mu\nu} ##, it has units of energy density. If, therefore, we know the total energy ##E## of the system described by ## T_{\mu\nu} ##, can we compute the volume of the system from ## V = E/T_{00}##? If it holds, I would assume this would...
  9. phyz2

    I Klein Gordon Invariance in General Relativity

    Hello! I'm starting to study curved QFT and am slightly confused about the invariance of the Klein Gordon Lagrangian under a linear diffeomorphism. This is $$L=\sqrt{-g}\left(g^{\mu\nu}\partial_\mu \phi \partial_\nu \phi-\frac{m^2}{2}\phi^2\right),$$ I don't see how ##g^{\mu\nu}\to...
  10. G

    A Understand (k,l) Tensors in Gen. Relativity

    In both Wald and Carroll, a type (k,l) tensor has k dual vectors and l vectors, yet a (1,0) tensor is a vector and a (0,1) tensor is a dual vector. I must be missing something simple. Please explain.
  11. spacecadet11

    I General physics question -- How can massless photons have momentum?

    P=mv *momentum equals mass X velocity. Light particles or "photons" are said to be "massless". And yet they have momentum. How is that possible? (p.s. I used to know the answer)
  12. The Bill

    Relativity Opinions on Rovelli's General Relativity: The Essentials?

    I recently noticed that "General Relativity: The Essentials" by Carlo Rovelli has been published. Based on the description, table of contents, and the Amazon reviews, it seems to me that it might be a spiritual successor to Dirac's "General Theory of Relativity." Is that an accurate assessment...
  13. P

    A Why are General relativity texts so much more formal?

    Hi all, What I notice is that there's a significant difference in style between the GR texts and the other textbooks. In particular, GR texts very much try hard to read like a math textbooks, emphasizing theorems and abstract definitions, which I'm not sure are practically useful (though...
  14. BadgerBadger92

    Relativity Good Beginner's General Relativity Books?

    I want to learn General Relativity so I am looking for a good beginners book with low amounts of math and clear explanations. Any suggestions?
  15. Z

    I Do Fictitious Forces Still Matter in General Relativity?

    hello it is well known that gravitationl force is actually a fictitious force generally speaking,are fictitious forces still necessary in general relativity ? the fictitious forces which we experience on a bus or on a car can also be understood as due to the spacetime distortion ?
  16. ergospherical

    Relativity "Must-read" papers in general relativity

    I found an interesting list of "must-read" papers in the field of general relativity compiled by Emanuele Berti: https://pages.jh.edu/eberti2/posts/must-read-paper-list/ Are there any notable exceptions, or other "classic" papers that - in your view - every relativist ought to have read?
  17. Thytanium

    A Radial Excess Calc: GR, 4πGρ & R00

    Which is the mathematical procedure to obtain ##\delta r = \frac{GM}{3c^2}## from ##\nabla^2 V = R_{00} = 4\pi G\rho## where ##\nabla^2 V## is volume contraction of a spherical mass of density ##\rho## and ##R_{00}## is the 00 component of Ricci tensor ##R_{ij}##?
  18. S

    B Time Dilation in a Galaxy: Calculating Mass Effects

    Hello everyone - The gravitational force near the edge of the galaxy at point A (see attached image) can be calculated by assuming that all the galactic mass is located in the center of the galaxy. - In order to calculate the gravitational force in the middle of the galaxy (point B) we take...
  19. Vividly

    Where can I take a general physics course 101 at online?

    Summary:: Where can I take a general physics course 101 at online? Looking for a general physics course that starts with algebra that I can do online.
  20. L

    I General solution of heat equation?

    We know $$ K(x,t) = \frac{1}{\sqrt{4\pi t}}\exp(-\frac{x^2}{4t}) $$ is a solution to the heat equation: $$ \frac{\partial u}{\partial t} = \frac{\partial^2 u}{\partial x^2} $$ I would like to ask how to prove: $$ u(x,t) = \int_{-\infty}^{\infty} K(x-y,t)f(y)dy $$ is also the solution to...
  21. karush

    MHB -2.1.1 DE Find the general solution

    [a] Find the general solution of $y^\prime + 3y=t+e^{-2x}\quad \dfrac{dy}{dx}+f(x)y=g(x)$ \$\begin{array}{lll} \textsf{Similarly} & \dfrac{dy}{dx}+Py=Q\\ \textsf{hence} & \mu(x)=\exp\left(\int f(x)\,dx\right)\\ \textsf{then} & \mu^\prime(x)=\exp\left(\int...
  22. karush

    MHB 2.1.2 Find the general solution of y'−2y=t^{2}e^{2t}

    Find the general solution of $y'−2y=t^{2}e^{2t}$ and use it to determine how solutions behave as $t \to \infty$ ok presume the first thing to do is to find $u{x}$ $\exp{\displaystyle\int{2} y}=e^{-2} or \dfrac{1}{e^2}$
  23. S

    I General Method for Mapping an Ellipsoid to Unit Sphere

    I have been working on a problem for a while and my progress has slowed enough I figured I'd try reaching out for some more experience. I am trying to map a point on an ellipsoid to its corresponding point on a sphere of arbitrary size centered at the origin. I would like to be able to shift any...
  24. ohwilleke

    I Scope of General Relativity: Assumptions & Implications

    Assumptions 1. General Relativity is the modern and most complete widely accepted theory of gravitation, formulated in a background independent, geometric way. 2. General Relativity is formulated in a manner consistent with Special Relativity and I could imagine that it might be possible to...
  25. korwynkim

    Intro Physics General introductory physics books compared to specific books on each topic

    What exactly is the difference in the way an general physics book (Halliday and Resnick, Young and Freedman) covers topics like mechanics, EM, and thermodynamics, compared to respective books like Kleppner and Kolenkow, Griffiths, and Schroeder, other than the amount of material covered for each...
  26. P

    Magnetic field - General current in a cube

    I could solve a similar (rather, a specific case of the above) where the current entered through a corner and left from the corner opposite to it along the body diagonal of the cube. For this specific case, I was able to easily exploit symmetry to deduce the answer (0). However, I cannot think...
  27. M

    I General relativistic comparison to Newtonian physics

    Let's say a small object orbits around massive object at some distance in perfectly circular orbit. In Newtonian physics the force acted upon orbiting body is: Force = m1 * orbital_speed^2 / distance = G * (m1*m2) / r^2 for an object of 1kg orbiting a body of 2*30^kg at the distance of 1.521 *...
  28. AHSAN MUJTABA

    I What is the confusion surrounding time as a coordinate in general relativity?

    We study metrics, in them, we take time as a coordinate. I mean to say that if time is a coordinate then in normal mathematical language, we can have negative coordinate values as well. This confuses me a lot as I want to see and understand the concept from the true physicist's perspective...
  29. Paulpaulpa

    Spacetime translations and general Lagrangian density for Field Theory

    In Sydney Coleman Lectures on Quantum field Theory (p48), he finds : $$D\mathcal{L} = e^{\mu} \partial _{\mu} \mathcal{L}$$ My calulation, with ##\phi## my field and the variation of the field under space time tranlation ##D\phi = e^{\mu} \frac{\partial \phi}{\partial x^{\mu}}## ...
  30. S

    MHB Mechanics- General motion in a straight line.

    It's the second question. Limiting equilibrium by a force of 5N means even friction is acting in the same direction. I don't understand how to calculate. Pls help
  31. S

    MHB Mechanics- General motion in a straight line.

    Iam not able to get the ans for q(a) which is 6.5 m/s I don't understand how to calculate (b)
  32. O

    I General solution of the hydrogen atom Schrödinger equation

    Hello everyone! I have two questions which had bothered me for quite some time. I am sorry if they are rather trivial. The first is about the general solution of the hydrogen atom schrödinger-equation: We learned in our quantum mechanics class that the general solution of every quantum system...
  33. hellow0rld

    Programs General Engineering/Chemistry/Biosciences/Physics - what to choose?

    Hey, I have some trouble deciding between 4 courses at the University of Sheffield (I am applying late, but there are still vacancies on all of these courses and as far as I know I can get a place at anyone of them). All of these courses are Foundation Year (FY) courses (they include an...
  34. S

    MHB General motion in a straight line

    I calculated (a) I don't know how to calculate (b)
  35. S

    MHB Mechanics- General motion in a straight line.

    A woman on a sledge moves in a straight line across horizontal ice. Her initial velocity is 2 m/s. Throughout the journey her acceleration is given by a= -0.01t m/s^2, where t is the time from the start in seconds. Find the distance that she travels before coming to rest. Iam getting the ans...
  36. S

    MHB Mechanics- General motion in a straight line.

    A goods train starts from rest at point A and moves along a straight track. The train moves with acceleration a m/s^2 at time t s, given by a=0.1t^2(6-t) for 0<t<6. It then moves at constant velocity for 6<t<156 before decelerating uniformly to stop at point B at t=165. Calculate the distance...
  37. M

    I Summation notation and general relativity derivatives

    Does $$\partial^\beta(g_{\alpha\beta}A_\mu A^\mu)$$ mean the same as $$\frac {\partial (g_{\alpha\beta}A_\mu A^\mu)}{\partial A^\beta} ?$$ If not could someone explain the differences?
  38. S

    MHB Mechanics- General motion in a straight line.

    A particle starts at the origin and moves along the X- axis. The acceleration of the particle in the direction of the positive x-axis is a= 6t-c for some constant c. The particle is initially stationary and it is stationary again when it is at the point with x coordinate = -4. Find the value of...
  39. S

    MHB General motion in a straight line.

    In q(c) I calculated the distance using t= 4.25 S . I get S=-3.23×10^-3 I added 5.78m to this which is the distance between A and B, I get 5.78m. Is this the correct method to prove that the bird returns to A. Pls help
  40. S

    MHB Mechanics- general motion in a straight line.

    I don't understand q(e) . Am I not supposed to calculate the distance between the interval 0 to 2? The textbook ans only shows the interval between 0 and 22. Should I calculate the distance taming only the second equation of velocity?
  41. S

    MHB Mechanics- general motion in a straight line.

    A particle moves in a straight line. The velocity of the particle, v m/s, at time t s is given by v= -t^3+9t m/s for 0<t<5 a) Find the displacement of the particle from its original position, when t=5s I got the ans for this by integration and limits 5 and 0 =- 43.8 b) work out the distance...
  42. S

    MHB Mechanics- general motion in a straight line.

    I calculated q(a)=1s q(b)=7cm I don't understand q(c)
  43. S

    MHB Mechanics- general motion in a straight line.

    S for 0 to 2s = 20m From 2s to 2.5s, I integrated v with limits 2.5 and 2 and got s=8.875m So total distance would be 28.9m but the textbook ans is 29.9m. Iam not able to get 29.9 m
  44. S

    MHB Mechanics- general motion in a straight line

    I don't understand how to find the distance that robot travels in 10s.
  45. cianfa72

    Two-port linear network general representation AV + BI = 0

    Hi, as follow-up to this thread I've a question about general representation of a two-port network. Basically it is ad hoc built four-terminal linear network (using controlled sources + nullator-norator pair): for it I found a general representation ##AV + BI = 0## as in the picture above. If...
  46. S

    MHB Mechanics- general motion in a straight line

    I don't know how to solve this
  47. S

    MHB Mechanics- general motion in a straight line

    I don't know how to calculate this. Pls help
  48. M

    I General relativity - covariant superconductivity, Meissner effect

    I am doing a project where the final scope is to find an extra operator to include in the proca lagrangian. When finding the new version of this lagrangian i'll be able to use the Euler-Lagrange equation to find the laws of motion for a photon accounting for that particular extra operator. I...
  49. S

    B Conservation Laws & General Relativity: Understanding Energy

    How does general relativity shows the conservation of energy. Because I was reading and listening to something today that touched on this subject. It almost seems as though if you scale GR to larger sizes it stops working and turns into an incomplete law of nature like Newton's laws of gravitation.
  50. H

    Other General Masters Advice after Bachelor's Degree in Physics

    I am in the second year of my Physics B.Sc and will soon have to make the decision how to continue from there. My grades are generally good, and I certainly want to continue my education, specifically a Masters. My goal is to be employed in industry, where I would strongly prefer actually...
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