What is Classical physics: Definition and 222 Discussions

Classical physics is a group of physics theories that predate modern, more complete, or more widely applicable theories. If a currently accepted theory is considered to be modern, and its introduction represented a major paradigm shift, then the previous theories, or new theories based on the older paradigm, will often be referred to as belonging to the realm of "classical physics".
As such, the definition of a classical theory depends on context. Classical physical concepts are often used when modern theories are unnecessarily complex for a particular situation. Most usually classical physics refers to pre-1900 physics, while modern physics refers to post-1900 physics which incorporates elements of quantum mechanics and relativity.

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  1. tellmesomething

    Need help interpreting a spring-block problem

    I haven't tried anything yet as im stuck at interpreting what the question asks itself. Firstly the only force acting on M1 support is the spring force (kx) why did it not move? Secondly is the reason of it not moving the fact that is also pulling the string with the same force (kx) so it is...
  2. PavithraSelvaraj

    I How Does Friction Function in the Movement and Turning of a Car?

    How can friction be responsible for all of these: stopping, moving and also turning a car? Does friction actually exist or is it something we assume because we don't know something about motion of objects? I have read a lot of discussions about friction and now it is a cloud of mess in my...
  3. DanCoimbra

    I Physical reality of nontrivial loops in SO(3)

    I will ask a mathematical and a physical-cum-philosophical question pertaining to the fact that SO(3) is not simply connected. Context Classical rotations in three spatial dimensions are represented by the group SO(3), whose elements represent 3D rotations. Having said that, note that classical...
  4. M

    I Gauss' law, method of images, and force induced on conductor plates

    Hi, I would very much appreciate some guidance on the below. Consider a one-dimensional world as depicted in the attached figure. We have two (lets say positively charged particles enclosed by two conductor plates. One plate is at ##x=0##, the other at ##x=L##. The particles are at ##x_1## and...
  5. L

    I Quadrupole moment tensor calculation for ellipsoid

    Determine the element ##Q_{11}## of the quadrupole tensor for a homogeneously charged rotationally symmetric ellipsoid, $$\rho=\rho_{0}=\text { const. for } \frac{x_{1}^{2}}{a^{2}}+\frac{x_{2}^{2}}{a^{2}}+\frac{x_{3}^{2}}{c^{2}} \leq 1 $$ The formula is $$Q_{i j}=\int \rho(\mathbf{r})\left(3...
  6. P

    Complaint Why Are Personal Theories Restricted on This Forum?

    Why can't you express a personal theory on these forums?
  7. K

    I Jonathan Oppenheim, "A postquantum theory of classical gravity?"

    in the news String Theory gets Competition: A New Attempt to Solve Physics' Biggest Mystery Sabine Hossenfelder based on Jonathan Oppenheim, "A postquantum theory of classical gravity?", Jonathan Oppenheim et al, "Gravitationally induced decoherence vs space-time diffusion: testing the...
  8. L

    I What causes the unexpected annihilation point in the Magic-Tee configuration?

    I have some problems understanding the magic-tee. There is a configuration for the E and H arm, where the signal output is blocked. As far as I understand you should be able to set one arm to 0 and the other to 1/4 of a wavelength, so the reflected wave's phase will be shifted by pi compared to...
  9. G

    I Taylor expansion about lagrangian in noether

    I was studying a derivation of noether's theorem mathematically and something struck my eyes. Suppose you have ##L(q, \dot q, t)## and you transform it and get ##L' = L(\sigma(q, a), \frac{d}{dt}\sigma(q,a), t)##. ##\sigma## is a transformation function for ##q## Let's represent ##L'## by...
  10. D

    Material to resist punch-through by metal rods

    TL;DR Summary: What would be the strongest material such pair of rods be able to punch through if the bottom of the rods was at 200 m from sea level and a platform with the strong material was at sea level, with 88,110 Kg on top of the rods? The following is just for fun, it doesn't need to be...
  11. MattRob

    I Atmospheric Density vs Altitude in an O'Neil Cylinder

    So, first off, for the uninitiated, an O'Neil Cylinder is a megastructure meant to be a space colony for humanity to live in in an Earth-like "outdoor" environment free-floating in space (ie, not on the surface of any celestial body with any significant gravity). It is essentially a cylinder...
  12. O

    Calculating Net Force on a Wheel: Magnitude and Direction | 0.350 m Radius

    Three forces are applied to a wheel of radius 0.350 m, as shown in the figure. One force is perpendicular to the rim, one is tangent to it, and the other one makes a 40.0 degree angle with the radius, and a 10 degree angle with the horizontal. a) What is the magnitude of the net force on the...
  13. E

    I An ID-card sliding on a low friction table

    I hold my identification card on a low-friction surface by one of its edges. I slightly lean it, and it starts to fall. Before it falls over, I place my finger against the card, and this prevents it from falling all the way over. Then, I withdraw my finger without pushing or pulling the card and...
  14. Z

    I Why is estimation of ##\frac{Pv}{RT}=1+BP+CP^2+...## interesting?

    Consider ##n## moles of a gas at a constant temperature ##T##. If we vary pressure ##P## and measure the corresponding values of volume ##V##, we can make a plot of ##P\frac{V}{n}=Pv## against ##P##. This gives us some graph which has some form. Turns out that for a range of pressure starting...
  15. Sibilo

    I Can EM waves stimulate neurons?

    I'm posting this topic after an invitation to do so. So considering that transcranial magnetic stimulation which operates in frequencies and therefore through EM induction can excite neurons, then can an EM wave also excite neurons?
  16. G

    I Transformations for isotropy in terms of math

    Probably, my last question about isotropy. This is the last thing that I want to double check. We know that mathematically, passive and active transformation are both the same. In passive, coordinate frame is moved and nothing else, while in active frame, objects are moved and coordinate frame...
  17. U

    I How find moment of inertia for car in turn?

    I understand what is moment of inertia is, flywheel with more mass at the edge has more inertia than flywheel that has mass closer to center. quote from link:https://decarreteres.wordpress.com/2019/04/24/chassis-engineering-polar-moment-of-inertia/ " We will only consider the engine and...
  18. Hak

    B Frequency of an EM wave in Classical and Quantum Physics

    In Classical Physics, when a charged particle oscillates, it emits an electromagnetic wave, and the frequency of the wave depends on the frequency with which the particle oscillates. But in Quantum Physics, when an excited atom emits a photon, the energy of the photon depends on the amplitude of...
  19. P

    I PIGA: Pendulous Integrating Gyroscopic Accelerometer

    Wiki describes the PIGA, https://en.wikipedia.org/wiki/PIGA_accelerometer. I want to see if I have a basic intuitive understanding of how it works. https://en.wikipedia.org/wiki/PIGA_accelerometer#/media/File:PIGA_accelerometer_1.png Lets imagine that the device, as shown, is at rest on the...
  20. deuteron

    Missing Algebraic Step in Three-Body Newtonian Problem

    TL;DR Summary: I am missing an algebraic step in the below described three-body problem, any help is much appreciated Consider the following setup where the distance between the masses are ##d##, and they exert gravitational force on each other. We want to find the angular velocity of the...
  21. G

    I Doubts about isotropy of space

    I might have some other questions related to this topic, but I will ask them in further replies. Isotropy of space is explained such as it should look the same in every direction. It's not enough to imagine ourselves to be in the center of the sphere, because definition says that to call space...
  22. G

    I Landau's inertial frame logic

    I had an interesting thought. Let's only look at the free particle scenario. We derive euler lagrange even without the need to know what exactly ##L## is (whether its a function of kinetic energy or not) - deriving EL still can be done. Though, because in the end, we end up with such...
  23. al4n

    B Moment of Inertia of Rectangles

    I often encounter the formula: I = (1/12)Mbh^2 when dealing with moment of inertia of rectangles and got confused when I was unable to get the same result when figuring it out with integration. It seems that the axis of rotation used is a line perpendicular to one of the bases and on the plane...
  24. A

    I need opinions on a Projectile Motion problem that I made up

    Recently I started making physics problems and I made one that I really like, but I would like some feedback from other people (how difficult it is, how enjoyable it is to solve this problem, what I could improve about it, etc). Here is the problem: A cannon is fixed at height H relative to the...
  25. Juanda

    I Balloon experiment - Classical Physics vs. Statistical Physics

    While reading a similar and deservedly closed post a contradiction came to my mind. The supposed contradiction is related to Statistical Physics where my understanding is only conceptual so correct me where I might be wrong. I remember reading that lightweight gasses can escape Earth's...
  26. Jenab2

    I Calculating the Raleigh Criterion constant to 99 significant figures

    I set about trying to use HiPER Calc Pro on my phone to solve the integral for the Bessel function of the first kind and of order one, so that I could get the ordinate value for the first root of the function to 99 significant figures, then divide that by π to 99 significant figures, in order to...
  27. T

    A Can position and velocity vary independently in Hamilton's Principle?

    To carry out the machinery of Hamilton's Principle though the calculus of variations, we desire to vary the position and velocity, independently. We proceed by varying at action, and set the variation to zero (I will assume ONE generalized variable: q1) In the above, I can see how we vary...
  28. G

    I How Does Landau Justify the Additivity of Lagrangians in Isolated Systems?

    Trying to grasp the Landau's book and struggling here. (Attaching the image).If you multiply L by some constant and put it in in the Euler-Lagrange equation, motion equation won't be changed. Q1: Though, what does he base his logic to say ##Lim L = L_A + L_B##. If we got 2 separated system, he...
  29. Feynstein100

    B Gas diffusion rates for methane into a vacuum versus into nitrogen

    Let's say I have a box with a partition dividing it into two halves. In one half, I have methane, in the other is pure vaccum. When I remove the partition, the methane will diffuse into the other half of the box and occupy the entire volume. This is the first case. In the second case, the setup...
  30. Joorge

    I Making a "Planetary Gear Set" using a 3D printer and PLA material

    I want to create a set of planetary gears using a 3D printer and PLA material. I'm designing them with the help of Autodesk Inventor 2020 since my knowledge in this area is quite limited. The gear set consists of a ring gear, a sun gear, and 2 planet gears. The sun and the ring gear rotate in...
  31. P

    B Looking for help Understanding Inertia

    Just a thread to see how inertia works, just studied the laws of motion, and have been fascinated with it.. could use some help on it tho :)
  32. H

    B Units of S/N ratio in some papers

    So this is a paper by Xavier Michalet and Shimon Weiss C. R. Physique 3 (2002) 619-644, showing that S/N ratio is given by equation (2). This is a fairly famous comprehensive paper on fluorescence microscopy, where other references regarding the same topic show the same equation more or less...
  33. ilasus

    B Thoughts about Galilean transformations

    Galilei transformations are a set of equations that describe how the coordinates of a point P change between two reference systems R, R' moving at constant speed v relative to each other. For example, when moving from the reference system R to R', the Galilei transformations are given by the...
  34. VVS2000

    A H-Theorem and Lagrange multipliers

    so I was studying H theorem from Richard Fitzpartic's site. https://farside.ph.utexas.edu/teaching/plasma/Plasma/node35.html Given H, they consider the following equation and set the constants as I want to understand how they got these particular values for a, b &c can we consider the...
  35. Rick16

    I Lagrangian approach for the inclined plane

    I want to use the Lagrangian approach to find the equation of motion for a mass sliding down a frictionless inclined plane. I call the length of the incline a and the angle that the incline makes with the horizontal b. Then the mass has kinetic energy 1/2m(da/dt)2 and the potential energy should...
  36. jselms99

    Einstein's Electrodynamics of moving Bodies

    Okay I’m assuming I have to use √1- v^2/c^2 multiplied by some coefficient of length but I don’t understand any of this and could really use help understanding the process and/or reference material that might point me in the right direction
  37. nish95

    Crosswind problem (pgs. 34-35, Thinking Physics, 3rd edition)

    Hi everyone, I was looking to develop my physical insight when I encountered this book by Lewis Caroll Epstein. For the crosswind problem, I couldn't understand the author's explanation; in particular, his concept of "artificial wind," and the force being larger in this case than the previous...
  38. R

    Equations of State in Modern Classical Physics (Thorne/Blandford)

    TL;DR Summary: Questions regarding the book "Modern Classical Physics" by Thorne/Blandford Hello, I'm going through this book and on pg. 127, regarding equations of state, there is a parameter, t (explicitly stated: "not to be confused with time"), that uses hyperbolic functions to relate the...
  39. S

    A Does the theory of information have anything to offer for physics?

    Is there any use for this concept in classical branches of physics? Can it be of any help for a physicist in resolving problems (or, at least, in resolving them more efficiently when compared with traditional methods)? The word «classical» means exactly that, i. e. mechanics, hydrodynamics...
  40. A

    Application Of Kirchoff Law (Desert)

    Homework Statement:: Sand is rough and black so it is a good absorber and radiator of heat depending on temperature. During the day, sand's radiation of the sun's energy superheats the air and causes temperatures to soar. But, at night most of the heat in the sand quickly radiates into the air...
  41. brochesspro

    Roundtrip by Plane: Understanding Wind & Velocity Effects

    The question I have is that if the aero plane is traveling in the same direction as the wind, would it not increase its velocity, as in with boats and streams? So, if by chance, ##w = v##, then the velocity of the aero plane would double. It feels weird as going by the same logic, if the speed...
  42. A

    B Is Relativity the Evolution of Classical Physics?

    Can someone please tell me what is Classical Physics? Does Kinematics in One Dimension such as in Physics textbook is considered a "Classical Physics"?
  43. VexCarido

    Projectile Intercept Math & Trigonometry

    Looking for some guidance on how to set up the equations for a projectile intercept given that you have perfect information about the target velocity, size and weather conditions in a 3D scenario, it's for an amateur videogame that I'm developing in my spare time For simplicity sake let's...
  44. OlegKmechak

    Is there some geometrical interpretation of force from Newton's Laws?

    dP = F dt dE = F dr or if we introduce ds = (dt, dr) (dP, dE) = F ds And both dP and dE are constant in closed system. Some questions: - How does its implies on definition of Force? - Is there some clever geometrical interpretation of Force? - Why P and E seems almost interchengable?
  45. Z

    Potential Gradient for individual charges and parallel plates?

    In my book, the potential gradient for a charge placed anywhere in space is defined as: E = -V/r HOWEVER, for parallel plate (capacitors) the potential gradient is defined as E = V/d (V being the potential difference). How come there's no negative sign for the potential gradient of the parallel...
  46. E

    B What are your favourite classical physics puzzles?

    ^ :wink: The title is pretty self-explanatory, wondered if people would like to share some fun problems that you can snuggle up to on a cold Winter's evening? Any difficulty level, but bonus points for problems which yield to elegant and/or creative solutions! Here's an example:
  47. VexCarido

    Runge-Kutta Projectile Approximation From Initial Conditions

    Hi everyone. I'm a new member, great to be here:) I have a few questions that I wanted to ask you guys regarding the method by which we implement the Runge-Kutta approximation of Projectile Motion if we should do it using a numerical iterative method with a Spreadsheet like Excel. I have...
  48. sahilmm15

    Classical Some books on introductory classical physics

    I need some suggestions on classical physics. You can help me with some high school papers or books to get started with.Thanks!
  49. dontknow

    Constraints in Rotation Matrix

    In Rigid body rotation, we need only 3 parameters to make a body rotate in any orientation. So to define a rotation matrix in 3d space we only need 3 parameters and we must have 6 constraint equation (6+3=9 no of elements in rotation matrix) My doubt is if orthogonality conditions...