What is Principle: Definition and 1000 Discussions

A principle is a proposition or value that is a guide for behavior or evaluation. In law, it is a rule that has to be or usually is to be followed. It can be desirably followed, or it can be an inevitable consequence of something, such as the laws observed in nature or the way that a system is constructed. The principles of such a system are understood by its users as the essential characteristics of the system, or reflecting system's designed purpose, and the effective operation or use of which would be impossible if any one of the principles was to be ignored. A system may be explicitly based on and implemented from a document of principles as was done in IBM's 360/370 Principles of Operation.
Examples of principles are, entropy in a number of fields, least action in physics, those in descriptive comprehensive and fundamental law: doctrines or assumptions forming normative rules of conduct, separation of church and state in statecraft, the central dogma of molecular biology, fairness in ethics, etc.
In common English, it is a substantive and collective term referring to rule governance, the absence of which, being "unprincipled", is considered a character defect. It may also be used to declare that a reality has diverged from some ideal or norm as when something is said to be true only "in principle" but not in fact.

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  1. Bloopy

    MATLAB: Verification of Superposition Principle

    Homework Statement Verify Superposition Principle using Matlab, given a DC source of 100V, an AC source of 50V, 60Hz and three resistances, R1=10 ohms, R2=20 ohms and R3=15 ohms. I created the circuit below and ran the program. Result: Homework Equations None, just running the program...
  2. F

    I Making sure about the spreads in the Uncertainty Principle

    Hello Forum, Going through Griffith's book last night, I read a good paragraph on page 111 about the canonical uncertainty principle for position and momentum in the x direction: $$\sigma_{x} \sigma_{p} \geq \frac{\hbar}{2}$$ If we could make 100,000 identical copies of a system in exactly...
  3. P

    I Why is the Uncertainty principle inherent to particles?

    If we have a particle, say, an electron and we shoot it straight through an empty box. This box is surrounded by light sources on its two sides: So, if you consider the above cube, if we shoot a particle in a straight line such that it crosses the face ABEF and it crosses the face HGDC through...
  4. Sandeep T S

    B Einstein's Lift Experiment: Unlocking the Principle of Equivalence

    In Principle of equivalence, we indroduce to the theoram by a lift experiment, my question is why the lift is fully closed one, why the observer in lift forbidden to observe out side world
  5. rishi kesh

    Derivative of -x using first principle

    Homework Statement This is a silly question,but i have a problem.How do we solve derivative of -x using first principle of derivative. I know that if derivative of x w.r.t x is 1 then ofcourse that of -x should be -1. Also it can be solved by product rule taking derivative of -1.x .Homework...
  6. K

    B Uncertainty Principle: Velocity, Position and Energy

    If velocity is delta position vs delta time and you know the velocity and change in time exactly why is it impossible to find the exact position of the electron? Same question for energy and position.
  7. DevonZA

    Hydraulic jack - Pascal's principle

    Homework Statement Homework Equations P1=P2 P=F/A F=PA F1/A1=F2/A2 F2 = F1(A2/A1) F2 = W(A2/A1) W=mg W=F*d The Attempt at a Solution A1= pi/4 * d2 = pi/4 * (0.15)2 = 0.0177m2 A2 = pi/4 * d2 = pi/4 * (0.05)2 = 0.00196m2 P1=P2 P=F/A F=PA F1/A1=F2/A2 F2 = F1(A2/A1) F2 = W(A2/A1)...
  8. Amaterasu21

    B Archimedes' Principle for gases - derivation?

    Hi all, I understand where Archimedes' Principle comes from in liquids: If we imagine a cylinder immersed in a liquid of density ρ whose cross-sectional area is A and whose top is at depth h1 and whose bottom is at depth h2: Force(top of cylinder) FT = ρgh1A Force(bottom of cylinder) FB =...
  9. Ben Geoffrey

    I Definite Integrals and the Principle of Least Action: Exploring the Connection

    This is with regard to my doubt in the derivation of the principle of least of action in Goldstein Is there any theorem in math about definite integrals like this ∫a+cb+df(x)dx = f(a)c-f(b)d The relevant portion of the derivation is given in the image.
  10. Michael27

    B Can the Holographic Principle make predictions

    I have been following the online lectures of Leonard Susskind regarding the holographic principle and entanglement.see Holographic Principle Lecture Part2 The universe can be seen as two-dimensional information on a cosmological horizon. (see https://en.wikipedia.org/wiki/Holographic_principle)...
  11. B

    Archimedes Principle and steel bar question

    Homework Statement Can someone tell me if i have done this correct please? A steel bar of length 0.6m and diameter 70mm is suspended from a chain and lowered into a tank of liquid whose relative density is 0.9. Determine the tension in the chain when the bar is fully immersed. The density of...
  12. J

    Principle of virtual work for continuous systems

    I always thought that the principle of virtual work (PVW) is valid for all structures, including continuous structures (like bars, beams, plates, etc.). However, in his book 'Fundamentals of Structural Mechanics', Hjelmstad states that the PVW is only valid for discrete systems with N particles...
  13. microsansfil

    I Noncommuting observables and indeterminacy principle

    Hi all, What is the link between noncommuting observables {\displaystyle [{\hat {A}},{\hat {B}}]={\hat {A}}{\hat {B}}-{\hat {B}}{\hat {A}} \neq 0} and indeterminacy principle (which is about inequality relation of standard deviation of the expectation value of observables A and B ) ? If the...
  14. Decimal

    Huygens-Fresnel principle of diffraction

    Homework Statement This question does not concern a homework problem but I don't really understand the Huygens-Fresnel principle of diffraction. My book states that an assumption is made that a wavefront acts as a source of secondary wavelets. They continue with the following derivation. This...
  15. P

    I Field operators and the uncertainty principle

    Hi, I am reading QFT by Lancaster and Blundell. In chapter 4 of the book the field operators are introduced: "Now, by making appropriate linear combinations of operators, specifically using Fourier sums, we can construct operators, called field operators, that create and annihilate particles...
  16. Isaac0427

    Pascal's Principle vs. Bernoulli's Principle

    Hi, There is a basic problem I am having with fluid dynamics that has been really confusing me. I have been told that as a result of conservation of energy and Pascal's principle, for an incompressible fluid Pin=Pout, or pressure is constant. However, pressure is not necessarily constant in...
  17. nomadreid

    I Holographic principle versus no-cloning

    If I understand the holographic principle for black holes correctly (which is highly unlikely, but this is a start), the information of a particle falling into a black hole is encoded on the event horizon. But from the view of General Relativity, the particle will not notice a change upon...
  18. Emmanuel

    Using Archimedes' principle in engineering applications

    Homework Statement A cylindrical buoy floats in sea water with its axis vertical so that it's three-fourths submerged. The buoy is 0.8m in diameter and 2m in height. Its fabricated from iron plate 10mm thick. Calculate the mass of iron chain securing the buoy. The relative density of iron is...
  19. Isaac0427

    I 2-particle Wavefunction and the Pauli Exclusion Principle

    Say you have two particles a and b with respective positions ##x_a## and ##x_b##. Particle a is in the state ##\psi_a##, and particle b is in the state ##\psi_b##. If they are distinguishable, the wavefunction is $$\psi=\psi_a(x_a)\psi_b(x_b)$$ However, if they are identical fermions, the...
  20. A

    Ratio of shear stress to normal stress along principle place

    Homework Statement "In a component under multi-axial state of stress, the ratio of shear stress to normal stress along principle places is _____. A) 0.0 B) 0.5 C) 1.0 D) 1.5 E)2.0" Homework Equations σx' = (σx+σy)/2 + ((σx-σy)/2)*cos(2θ) + τxy*sin(2θ) σy' = (σx+σy)/2 - ((σx-σy)/2)*cos(2θ)...
  21. Y

    MHB Combinatorics - The pigeonhole principle

    Hello, I am trying to solve a problem related to natural numbers. The solution is based on the pigeonhole principle, however I can't see the connection. The is the problem: Choose 12 two digit numbers. Divide each by 11 and write down the residue (i.e. do the modulu operation). Group the...
  22. e2m2a

    I An exception to the principle of equivalence?

    Not sure of the dynamics of the following situation. Suppose there is a mass that can slide on a straight track with one degree of freedom. Assume no friction in this scenario. On top of this mass is a track that forms a quarter circle. On this track is a sphere that can slide(again assume...
  23. M

    How Does Bernoulli's Principle Apply to Varying Pipe Diameters and Water Flow?

    Homework Statement A horizontal length of pipe starts out with an inner diameter (not radius!) of 2.60 cm, but then has a tapered middle part which narrows to a diameter of 1.60 cm. When water flows through the pipe at a certain rate, the gauge pressure is 34 kPa in the first (wider) section...
  24. F

    I Inertial & non-inertial frames & the principle of equivalence

    One particular form of the equivalence principle states that The laws of physics for freely falling particles in a gravitational field are locally indistinguishable from those in a uniformly accelerating frame in Minkowski spacetime My question is, does one arrive at this conclusion from a...
  25. F

    I Questions about the general principle of relativity

    One of the founding principles in GR is the principle of general relativity, which loosely states that all coordinate frames (inertial and non-inertial) are equivalent in the sense that the laws of physics are invariant. My question is, does the justification for this come from Einstein's...
  26. F

    I Understanding the Einstein Equivalence Principle

    The Einstein equivalence principle (EEP) states that “The outcome of any local non-gravitational experiment in a freely falling laboratory is independent of the velocity of the laboratory and its position in spacetime.” I’m trying to make sure I’ve understood this correctly. I’m I correct to...
  27. R

    B Possible Loophole in the uncertainty principle

    The uncertainty principle states that anyone given person who knows a lot about a given particles velocity will know less about the location, but if then they try to observe the location, the less they will know about the velocity. What if two scientists observed one particle though. One...
  28. M

    Infrared thermometer working principle

    So, as far as I understand IR thermometer works by measuring light irradiance coming from an object (in the IR spectrum) and then calculating the object temperature using Stefan's law. Since the irradiance falls like 1/r2 with distance, I am wondering how it takes distance into consideration...
  29. W

    How does the Pauli Exclusion Principle in this problem?

    Homework Statement This is not a homework problem. It's an example in a textbook. 3 electrons. For ##S=3/2##, we have that $$ m_{s_1} = m_{s_2} = m_{s_3} = 1/2 $$ Therefore by the Pauli Exclusion principle, $$ m_{l_1} \neq m_{l_2} \neq m_{l_3} $$ and they take the values ##-1,0,1##...
  30. B

    I Clock hypothesis, gravity time dilation and Equivalence Principle

    1. The Clock Hypothesis states that the rate of a clock does not depend on its acceleration but only on its instantaneous velocity. This has been experimentally verified at very high accelerations. 2. A clock in a gravitational field experiences time dilation and runs slower that one not in a...
  31. T

    I How does a faucet use the Venturi principle

    I've noticed that a slight opening of the faucet releases less water which makes sense intuitively but I don't notice an increase in velocity. Since a slight opening in the stopper would be a convergence in cross sectional area. Am I missing something? I read about resistance affect but still...
  32. R

    B Pauli's exclusion principle

    So my question is why can't 2 object be at the exact same potion, (i.e. overlap). Why can't a +ve quark and electron just merge. In an universe where there is no force caused due to charge, why can't we just walk through a solid wall.
  33. S

    I Spinning disk, length contraction, & equivalence principle

    Suppose we have a spinning disk with a very fast spin, an observer in the center, and an observer on the edge. Suppose that the observer on the edge measures the circumference of the spinning disk. (1) Now, the observer on the edge at a given instant will be moving at a faster speed than the...
  34. Erland

    Trouble with Bernoulli's principle

    I have some trouble with the derivation of Bernoulli's principle. The Wikipedia gives two derivations, for an incompressible fluid, and I have trouble with both of them: https://en.wikipedia.org/wiki/Bernoulli%27s_principle#Derivations_of_the_Bernoulli_equation In the first derivation, using...
  35. anorlunda

    KISS Principle Marine Propulsion

    I"m a big fan of the KISS principle in engineering. I'm also a boater. I just found something I wanted to share. It is a permanent magnet motor in which the propeller itself is the rotor. The video hints that it works with simple reversals of polarity similar to a stepper motor. That...
  36. N

    Proving Fermat's principle without calculus?

    According to me this topic must be raised and discussed how fermat did it without calculus.What problems he faced since calculus was developed afterwards by Newton leibniz. http://aapt.scitation.org/doi/10.1119/1.1514235 Moderator's edit: File substituted by link due to potential copyright...
  37. J

    Heisenberg's indetermination principle and Ccopenhagen interpretation

    Ive been doing some researches about QM and I am in a condition where i can't differ Heisenbergs indetermination principle from copenhagen interp. Can somebody please explain simply or advancedly(?) (in an understandable way) are there any differences between them. If there are, what are those...
  38. D

    I The uncertainty principle and moving reference frames

    To what extent is the Heisenburg Uncertainty principle a statement about moving frames of reference? The ill-defined position of a particle seems to imply that one can never find an inertial frame of reference in which the velocity of a given particle is constant.
  39. T

    Maximum entropy principle from minimum energy principle

    Homework Statement Formulate a proof that the energy minimum principle implies the entropy maximum principle. That is, show that if the entropy were not maximum at constant energy then the enrgy could not be minimum at constant entropy. HINT: First show that the permissible increase in entropy...
  40. Gio83

    A Derive the Bianchi identities from a variational principle?

    Einstein's field equations (EFEs) describe the pointwise relation between the geometry of the spacetime and possible sources described by an energy-momentum tensor ##T^{ab}##. As well known, such equations can be derived from a variational principle applied to the following action: $$S=\int\...
  41. A

    Archimedes' Principle and a weather balloon

    Homework Statement 2. Homework Equations Buoyant force= mg(mass of fluid displaced = Vpg (volume of fluid displaced) Buoyant force=weight of object (if floating) The Attempt at a Solution If the total mass is 99kg, then the total force acting downwards is 990N. It also said that the balloon...
  42. Marrrrrrr

    A Virtual Fermions and Pauli Principle

    Hi guys, Do virtual particles, when they are fermions, obey Pauli exclusion principle as real fermions do? More specifically, what I am wondering is the following: Fermion fields would have some energy at every point in spacetime due to the uncertainty principle. Now, is it possible for the...
  43. PrathameshR

    I Derivation of Euler Lagrange's equations from D'alemberts principle

    In the derivation given in Goldstein's book it is given I can't understand from where it comes. It's not at all trivial for me but it's presented as if it's trivial.
  44. A

    I Principle of superposition of states

    Upon reading Landau QM, the Principle of superposition of states, I got confused. It states (and i quote): "Suppose that, in a state with wave function Ψ1(q), some measurement leads with certainty to a definite result 1, while in a state with Ψ2(q) it leads to a different result 2. Then it is...
  45. davidge

    B Einstein's Equivalence Principle: What's New?

    The equivalence principle states that the laws of physics are the same in any inertial frame. Translating this into mathematics language, the equivalence principle states that a given equation should retain its form when one transform between the coordinates of two intertial frames, correct...
  46. C

    I Huygens principle from Kirchoff Integral (sign doubt)

    Consider the Kirkoff integral theorem and the Huygens -Fresnel principle/formula (both from Wikipedia): KIT The Kirchoff integral for monochromatic wave is: $$U({\mathbf {r}})={\frac {1}{4\pi }}\int _{S'}\left[U{\frac {\partial }{\partial {\hat {{\mathbf {n}}}}}}\left({\frac...
  47. C

    How Can Bernoulli's Principle be Related to Fire Hoses

    Hello everybody: I am trying to test, using Bernoulli's Principle, when firehoses are most effective. I know this is extremely broad, but does anyone have any ideas for independent variables? I am thinking about the the width of the end piece of the nozzle... Any help/guidance would be...
  48. S

    I Applying the Principle of Relativity to Quantum Mechanics

    I read the forum rules, I hope I am not breaking them as these principle is generally accepted and I am not contradicting mainstream science. "The principle of relativity, according to which the laws of physical phenomena should be the same, whether for an observer fixed, or for an observer...
  49. D

    B Does Heisenberg's uncertainty principle imply no free will?

    Does the Heisenberg uncertainty principle mean that some particles do not have law-determined properties like position and momentum, or does it mean that their properties cannot be measured accurately? In other words, do all particles have a certain position and momentum at time t? This question...
  50. Karolus

    B Superposition principle: clarifications

    What is the "superposition principle"? I have a confusion about one of the fundamental concepts of quantum mechanics, the principle of superposition This sounds, more or less: a linear combination with arbitrary coefficients of different quantum states is a new quantum state If I have (for...
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