Principle Definition and 1000 Threads

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. R

    Application of Heisenberg Uncertainty Principle

    Homework Statement A parallel beam of electrons traveling in x- direction falls on a slit of width d. If after passing the slit, an electron acquires momentum py in the y direction then for a majority of electrons passing through the slit A. |py|d ≈ h B. A. |py|d > h C. |py|d < h D. |py|d >> h...
  2. Z

    Simple Conceptual Question Regarding Pascal's Principle

    Homework Statement There's a conceptual question I've encountered in my reading, wherein we're supposed to determine the validity of a statement: "According to Pascal’s principle, if you increase the pressure enough so that the force at one end of an oil-filled tube increases by 10 N, the force...
  3. N

    Complex Analysis: Open Mapping Theorem, Argument Principle

    Homework Statement In each case, state whether the assertion is true or false, and justify your answer with a proof or counterexample. (a) Let ##f## be holomorphic on an open connected set ##O\subseteq \mathcal{C}##. Let ##a\in O##. Let ##\{z_k\}## and ##\{\zeta_k\}## be two sequences...
  4. DaTario

    Can Huygens Principle Be Applied to Waves on a String with Fixed Ends?

    Hi All, Is it correct to apply Huygens Principle to a situation in which a wave propagates in a string with fixed ends? I know Huygens principle is related to regular propagation e superposition properties of waves, and all these can be found in the string context, but I am not sure this...
  5. S

    Almost sure invariance principle

    I would like to understand the Almost Sure Invariance Principle: "We say that the functions f_i: [a,b] →ℝ satisfy the Almost Sure Invariance Principle with error exponent γ < 1/2 if there are a probability space supporting a Brownian motion B and a sequence ξ_i, i ≥ 1, such that (1) {f_i}_{i≥1}...
  6. Chemer

    How Does the Pauli Exclusion Principle Limit Electron Spin Directions?

    Hi, Can someone please explain this to me? "The axis of rotation for a non-quantum-mechanical object can point any way it likes. The Earth could rotate around an axis ninety degrees from the current one, so that the North Pole always faces the sun and the South Pole always faces away from it...
  7. Jimster41

    Understanding the equivalence principle

    Mentor Note: This thread has been separated out of a previous one to keep discussion of this particular topic open, since the previous thread has been closed. Sorry, the opportunity to ask questions is just too hard to resist. I'm still searching for the right understanding of equivalence. Or...
  8. Praveen Vijayan

    Uncertainity Principle: possible to know the momentum and position?

    The principle states it is impossible to 'simultaneously' know the position and momentum(velocity)of an object. Position is something that can be noted at a particular instant, as from a photograph whereas velocity is something that can only be measured over a period of time,as from a movie. The...
  9. danielng245

    Please help calculate flowrate frm blower to push water down

    How to calculate how much flowrate from blower i can push water pool 2,75m*1,8m down by 1,25m in 1 sec? Note : Blower Pressure 0.03 bar - 0.035 bar There is an empty room above the water pool with dimension of 2.75m*1.8m*1.7m This process happen in a closed chamber...
  10. M

    MHB Solve the Pigeonhole Principle Problem w/ PHP

    Ran across this problem reading another forum, and wonder if PHP allies here. Given a set $X$ of 16 positive distinct integers, you can find non-empty, disjoint subsets $A, B \subset X$ such that $A$ and $B$ have the same number of elements, and $|\alpha - \beta| < 0.0025$, where $\alpha =...
  11. Shreyas Shree

    Philosophy of the Uncertainty Principle

    what are the philosophical conclusion one can arrive at from the Uncertainty Principle?
  12. N

    Bernoulli's principle and work energy theorem

    for a stream line flow of ideal liquid (non-viscous) imcompressible the sum of pressure energy per unit volume kinetic energy per unit volume , potential energy per unit volume remains constant mathematically P+1/2roV2+ROGH=constant consider a fluid flowing in a pipe of various crossections we...
  13. Misha Kuznetsov

    Uncertainty Principle of a high speed particle

    Hello everyone, Heisenberg's Uncertainty Principle states that the less uncertainty there is of a particles position, the more uncertainty there has to be of its momentum. Since mass is a constant in this case, we can refer to the uncertainty of the velocity instead. I was reading a physics...
  14. Last-cloud

    Obtain Equation Using Hamilton's Principle

    I want to obtain equation using Hamilton principle but I just couldn't figure it out; i have The kinetic energy : \begin{equation} E_{k}=\dfrac{1}{2}m_{z} \displaystyle\int\limits_{0}^{L}\ \left[ \left( \dfrac{\partial w(x,t)}{\partial t}\right)^{2}+\left( \dfrac{\partial v(x,t)}{\partial...
  15. D

    Principle of corresponding states

    Homework Statement Show that it is always possible to adjust measurement units such that a; b can be assigned any values you want. This means that e.g. all van der Waals gases look exactly the same if the units are accordingly adjusted. (This is what is called principle of corresponding...
  16. L

    Is There Buoyancy on a Sealed Metal Cube in Water?

    Homework Statement I have confusion. Suppose i have metal cube placed in empty vessel. I have seal tight the base of cube so that the water or any fluid can't seep below the cube. Now i pour water into the vessel. Will there be bouyancy on the metal cube ?? If i measure the weight of cube, will...
  17. J

    Bernoulli's Principle and Energetics of Flowing blood

    My understanding and application: Flowing blood with mass m, and velocity v has KE proportional to mean velocity squared as blood flows inside the vasculature, pressure is also exerted laterally against the walls of the vessels So, it is then reasonable to use Bernoulli's for the blood and...
  18. B

    Calculating the displacement using the work-energy principle

    Homework Statement An object is traveling at 10m/s. along an inclined surface of an angle 10°. How far does it go up the bank? How fast will it be going when it travels back down? Coefficient of friction is .15 Homework Equations Ei = Ef Ef - Ei = Eloss [/B] W = Fd The Attempt at a Solution...
  19. Coffee_

    Problem with understanding Babinet's principle

    I'm having some trouble with understanding Babinet's principle, which in a simple case should imply the following: ''If I send light through a single slit, then I observe a certain diffraction pattern at the screen. Now I replace the slit with a single obstruction of the same width as the slit...
  20. mtnsrfr

    Uncertainty principle for time-energy & momentum-position

    Homework Statement 1) Very short laser pulses can be produced, on the order of a few femtoseconds. (look it up.) If a laser has a center wavelength of 800nm, and lasts for 20 femtoseconds, (2*10-14s) what spread of wavelengths must it have to be compatible with the time-energy uncertainty...
  21. A

    Uncertainty Principle cause infinite wavefunction solutions?

    Dear Physics Forum, Is the Uncertainty Principle the cause of the infinite solutions to Schrodinger's equation? I get the sense it is not. Could you elaborate a little? Thanks, Mark
  22. S

    Question on validity of Heisenberg's Uncertainty principle

    Hi, I have a question about the validity of Hiesenberg's principle when relativity is in action. Hiesenberg's principle tells us that simultaneous measurement of position and momentum can not be done accurately . But relativity tells us that simultaneity is relative , so simultaneous...
  23. M

    Maxmimum\Minimum modulus principle

    Hey guys, I'm studying for an exam that I have in Complex Analysis and I got stuck at the following question. Question: True/False f(z) is an analytical function in the ring 1 =< z =< 3. Also, the minimum of |f(z)| on |z|=1 equals to 1 and the maximum of |f(z)| on |z|=3 equals to 2. Therefore...
  24. T

    About the Uncertainty Principle

    If I understand correctly, this very important principle in quantum theory says that the more precise you know the position of a particle, the less precise its momentum can be known. So this raises several questions to my mind: 1) Does this principle applies to photons? Isn’t a photon source...
  25. J

    MHB How to Differentiate y=x^x by First Principles?

    Anyone know how to differentiate y=x^x by first principles?
  26. S

    Uncertainty principle presentation

    Hi all. In my physics class I have to give a 15 minute blackboard lecture on a topic in modern physics. I chose the uncertainty principle because I feel there is a tendency (at least at the undergrad level) to just accept what it is without proof or intuition. I would like to go into greater...
  27. F

    Trouble understanding Fermat's principle of least time

    I've been reading about Fermats last principle in Feynmans lectures on physics, and he sort of goes through the derivation of Snell's law by considering a simple refraction and applying a bit of trigonometry (see photo). What I'm having trouble with is this. He states that if you take a two...
  28. Calpalned

    Principle of Equivalence and Acceleration in Deep Space

    Homework Statement I know that the principle of equivalence states that a person in a window-less box will not be able to tell if s(he) is in a stationary box on Earth or in a box that is accelerating upward at a constant rate. I am assuming that the acceleration of the rocket is 9.8 m/s^2...
  29. G

    Superposition Principle to Solve Circuit

    Homework Statement Homework Equations KVL: ΣV = 0 KCL: ΣI = 0 v = iR The Attempt at a Solution I started by removing the independent current source to leave an open circuit. Then I attempted nodal analysis at nodes v1, v2, and v3: KCL @ v1: (v1 - v2)/10 = v1/40 KCL @ v2: (v2 - v1)/10 -...
  30. J

    Electric dipole equivalence principle paradox?

    Imagine an electric dipole with charges ##+q##, ##-q##, mass ##m## and size ##d##. Assume this dipole is oriented horizontally and is sitting at rest on top of some weighing scales on earth. As the charges are at rest the weight of the dipole is just ##-mg##. But by the principle of...
  31. E

    Equivalence Principle Test Kits

    I'd like to see for myself the Equivalence Principle. Would there be a commercially available test kit like perhaps a small iron and cotton enclosed in vacuum tubes and they are to fall at same time and hit the bottom at same time with indicator lights to tell if they hit at same time or at bit...
  32. H

    Principle and Angular Momentum Quantum Numbers

    My understanding of the angular momentum quantum number is that a different number indicates a different region of space that the electron can occupy. So does the principle quantum number determine the size of that region? For example, is 2s the same as 3s in shape, but the 3s has a greater...
  33. D

    Better Equivalence Principle Explained

    I am new to relativity, so bare with me. I do not want to argue against it; however, one must admit it is a rather awesomely unwieldy theory. In my self education on the subject, I am bothered by the Equivalence Principle, mainly this: An elevator accelerating through space is no different from...
  34. B

    Uncertainty principle and relativity

    Consider a particle and you measure the position with a relatively small uncertainty in a box Δx2 . And then you measure the momentum very precisely, let's say with infinite precision. Is the position then completely undetermined or is it still in a large ball of 4/3π(cΔt)3? Does the wave...
  35. Rajkovic

    Is Everything Connected by Quantum Entanglement?

    Hi, I have 16 years old, I am planning to be a physicist in the near future, and I have 3 doubts, could you guys answer to me? 1. Does quantum entanglement proves that everything is connected? http://phys.org/news/2015-01-popper-againbut.html#nRlv 2. 'The Observer Effect' and 'The Uncertainty...
  36. T

    Superposition principle for potential?

    Homework Statement A solid, conducting sphere of radius "a" and charge -Q is concentric with a spherical conducting shell of inner radius "b" and outer radius "c". The net charge on the shell is +3Q. Take the zero of electric potential to be at some point at infinity. a.) Use Gauss's law to...
  37. Palpatine

    How to devise an experiment that violates uncertainty principle

    Lets suppose device A measures the position of a particle very accurately. Device B now cannot measure its momentum to high accuracy due to the uncertainty principle. But let's suppose that neither A nor B can ever communicate their findings to the rest of the world. Now the uncertainty...
  38. I

    Holographic Principle question

    So I've been looking up things on the Holographic Principle for a while now, but there's still a few questions I have. As I understand it, the Principle says that if I drop a book into a black hole the book's information would be 3D inside the black hole and it would also be 2D on the event...
  39. K

    Chemical Equilibrium and Le Chatelier's Principle

    Homework Statement Without adding any Chromium based compounds, how would you manipulate the above equation to produce more CrO42- ions? Be sure to use chemical equations to show the answer. Homework Equations 2CrO42- (aq) + 2H3O+ <--> Cr2O72-(aq) + 3H2O (l) The Attempt at a Solution So my...
  40. H

    Equivalence Principle: Feel Difference Between Situation A and B?

    Here are the 2 situations: Situation A: a person floating in space far away from any mass (i.e. the person is in zero-gravity environment) Situation B: a person undergoes a free-fall from the top of a roller coaster (assuming that there's no air resistance) My question is, would the person in...
  41. V

    Superposition principle and information

    I have a question about, perhaps, GCSE level physics, if not below, which, for some reason, is not explained anywhere I've looked up. Or, at least, I didn't find any explanation. The picture above is supposed to explain the concept of superposition. It depicts a pair of one-dimensional waves...
  42. N

    How did we arrive to Hamilton's principle ?

    Hi. The Lagrange equations can be derived simply by using Newton's laws and defining potential, work and kinetic energy. So that's just a mathematical reformulation of known results. Is it the same with Hamilton's principle? Is the concept of "action" and it being stationary just another...
  43. Saumya Kar

    Von Mises stress Vs Principle stress

    Hello Folks, May be I am bring up the old topic again., but I've lost enough sleep over this topic. I understand that we use Von-Mises criteria for ductile material failure by comparing to yield limit and max principal stress is used to check failure for brittle materials. My question is bit...
  44. P

    How Does Le Chatelier's Principle Affect Reactions in Chlorine Water Systems?

    Cl2(g) + H2O(l) = HCl(aq) + HClO(aq) (reversible reaction) 1. What would happen to the concentration of HClO if more HCl was added? Wouldn't it decrease, since the position of equilibrium then would shift to the left? 2. If NaOH was added to neutralize the acid, what would happen to the...
  45. O

    Principle of linear momentum for a rocket

    Homework Statement vertical rocket start: F_thrust (simple F) Δm (fuel consumed per Δt) m_tot the relative velocity of the gas w is demanded. Homework Equations vgas=v+Δv+w, w<0 m(t)=mtot-Δm*t The Attempt at a Solution rocket acceleration. F-G=m(t)*a(t) a(t)=F/m(t)-g first...
  46. rumborak

    Information as the key underlying physical principle

    It seems to me, at least when it comes to quantum mechanics, "information" has become the most basic unit. Like, quantum entanglement works to the point that information is extracted, and one can even revert certain things by making sure the information is destroyed. Same with the discussion...
  47. rpthomps

    Heisenberg's Uncertainty Principle using Linear Algebra

    I am working through linear algebra from MITs MOOC online courses. One of the question refers to the uncertainty principle. It states: AB-BA=I can happen for infinite matrices with A A=A^{ T }\\ and\\ B=-B^{ T }\\ Then\\ x^{ T }x=x^{ T }ABx-x^{ T }BAx\le 2\parallel Ax\parallel \parallel...
  48. M

    Calculate Tension in Rope: Principle of Moments Homework

    Homework Statement Calculate the tension in the rope, T, in the diagram below: http://imageshack.com/a/img905/2848/yMC01l.png Homework EquationsThe Attempt at a Solution The 'beam' is a stable structure, thus the resultant forces be equal that are acting upon the beam. So, I calculated the...
  49. J

    Proof of the linearity principle for a 2nd order PDE?

    Homework Statement My textbook (Advanced Engineering Mathematics, seventh edition, Kreyszig) indicates that if u1 and u2 are solutions to a second-order homogeneous partial differential equation, and c1 and c2 are constants, then u where u = c1u1 + c2u2 is also a solution, this is the...
  50. DiracPool

    GR Journal: Equivalence Principle & Tidal Forces

    Say we have an elevator moving through deep space at a constant velocity. We have a light emitter at the "top" of the elevator pointing towards a detector at the bottom of the elevator. We shine the light and notice that the frequency at which the light was emitted at the top is the same as...
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