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. R

    Conservation of Mass Principle applied to Refrigerators

    Dear all, Can the conservation of mass principle be applied to the mass flow rate of a refrigerant in an ideal refrigerator system? And what about for an actual refrigeration system? I'm reading the principle here but can't work it out. Says that it applies for steady flow, but I assume...
  2. S

    Is the totalitarian principle the key to understanding limitless possibilities?

    The totalitarian principle states that 'every process that is not forbidden must occur'. Isn't this principle self-obvious? After all, a process that is not forbidden can, by definition, occur. But, I think I am missing a layer of meaning implied by this statement. If that is so, would you...
  3. S

    Understanding the Pauli Exclusion Principle

    When a fermion x approaches another fermion y does x send out bosons to y which tell it to get out of the way? In short, how does y know to get out of the way of x?
  4. M

    Operating principle of a Six Phase induction motor

    Hi Sir, I have seen in many IEEE magazines that, a six phase induction motor is having two 3 phase windings spatially separated by an angle of 30 degrees electrical. I have attached the 6 phase induction motor diagram. But I am not able to understand how the motor operates i.e. how the rotor...
  5. F

    Understanding the Flow Control Principle of Valves

    How exactly would you describe the principle of a valve for flow control? In a globe valve for example the fluid flows through valve seat and generally leaves the valve with the outlet diameter being the same as the inlet diameter. My original assumptions were that Bernoulli's principle...
  6. S

    Can uncertainity principle be tweaked

    I am new to quantum mechanics. By hitting a particle with photon in vacuum we find its momentum and then again hit it with another photon to find its position . can we calculate backwards using conservation of momentum the position an momentum of that particle in both two states ( since we know...
  7. S

    Principle of conservation of linear momentum equation

    Homework Statement A massless spring attached to a wall lies on a frictionless table. It has a block of mass 2kg attached to one end, initially the block is at rest. Another block, also of mass 2kg is sliding on the table top with a speed 8m/s. At t = o the moving block collides with the...
  8. S

    Mach's Principle: What Is It & How Can I Understand It?

    I learned about mach's principle from a book. But I can'understand the details of it. So can you please explain me what is mach's principle? Is it correct?
  9. T

    Application of the Argument Principle

    I've been studying for a test and have stumbled upon another type of problem I'm not comfortable with yet. I need help applying the argument principle - the practice problems in my textbook all consider only polynomials in the first quadrant. In solving this type of problem I consider...
  10. N

    Boson statistics and the uncertainty principle

    This question is regarding the boson statistics and it’s relation to the uncertainty principle. Consider we have a vacuum state and we apply a field operator on it to create a particle at position x, we end up with state like \begin{array}{l} \left| \psi \right\rangle = {\psi ^\dag...
  11. M

    Can someone prove the uncertainty principle for me

    My qm textbook, aptly named "quantum mechanics", is by McIntyre, though it omits the proof for the uncertainty principle and simply states it as ∆A∆B ≥ 1/2|〈[A,B]〉|. In words, if that's unclear, this is 'the product of the rms deviations of A and B is greater than/equal to one half the absolute...
  12. D

    We know that superposition principle is valid in Quantum Mechanics

    because Schrodinger equation is a linear differential equation. How do we show that Schrodinger equation is a linear differential equation?
  13. D

    Statistical physics reflection principle

    Homework Statement Consider a random walker in one dimension, which can take right or left steps with equal probability. Assume that the walker starts at the location k>0 and there is an absorbing wall at point labelled as 0, that means if the walker reaches 0 the process stops and he stays...
  14. P

    Bernouilli's principle pipe flow problem

    Homework Statement On a horizontal pipe with flowing water on point 1 there is a vertical pipe with water up to some point. On another point 2, we have a pitot tube (L shaped) against the water flow and the lever on the vertical part is higher that on point 1. If the water flow stops what...
  15. K

    Rigid Box Particle and Heisenberg Principle

    Homework Statement For the ground state of a particle in a rigid box, we have seen that the momentum has a definite magni- tude (h/2π)k but is equally likely to be in either direction. This means that the uncertainty in p is Δp≈ (h/2π)k. The uncertainty in position is Δx≈ a/2. Verify that...
  16. T

    I understanding Archimedes' principle.

    I want to know why does the buoyant force equal to the weight of fluid displaced and how the weight of water displaced is equal to the weight of object for free floating objects? What's buoyant force by the way?
  17. K

    Fermat principle and Euler-Lagrange question

    Hello, The Fermat principle says that (***) Δt = (1/c) ∫ μ(x,y) √1+y'2 dt Say, we are studying a GRIN material where the refraction index is μ = μ(x,y) and want to figure out the shape of the ray trajectory y=y(x). Here is what I know (this is not a homework question) but am unsure if...
  18. N

    Reconciling quarks and the uncertainty principle

    As a result of some precise experimental data, we now know that the mass of the quark is not naively 1/3 the mass of the proton. The most recent estimates for the mass of the quark is: Masses of the current quarks: = 2 - 8 MeV/c2 = 1.0 - 1.6 GeV/c2 = 168 - 192 GeV/c2...
  19. D

    2 Atomic Physics questions - Pauli exclusion principle

    Homework Statement Q1. Briefly explain the relevance of the Pauli exclusion principle for the structure of the periodic table of the elements. Q2. What is the maximum number of electrons that can be located in an atomic subshell with quantum numbers n and L? Briefly expain your answer...
  20. E

    Mach's principle, GR and the nature of space

    I have been puzzled by this for years, so I would welcome some enlightenment. It seems that Einstein was enamored with Mach's principle while searching for GR, but in the end GR does not seem compatible with it - or rather has nothing to say about it. What I mean is that the proverbial...
  21. S

    Info required about working principle of solar panel.

    Hi; Normally, the solar panel charges a 12V battery and battery provides backup to load via an inverter. The solar panel produces voltage which is directly proportional to sun light. So early in the morning and in evening, solar panel produces less voltage which is insufficient to charge the...
  22. B

    Principle of Least Action via Finite-Difference Method

    I have to be honest, the principle of least action seems to me more of a religious claim one takes on complete faith, though of course I'm hoping this is just because I don't understand it. I tried to explain this to a friend suffering through a mechanics class & was literally pushed to say 'one...
  23. W

    Duality Principle | Understand the Concept

    Have i done it correctly?
  24. E

    Entropy increase,coarse-grained vs. Landauer's principle justification

    First off, just clarify that I have a very, very superficial knowledge of Physics, so my apologies if my question is based on an obvious misunderstanding of the basic principles underlying the second law of thermodynamics or if it has a rather simple answer. The doubt that I have is related...
  25. H

    Argument principle for a rectangle

    Homework Statement . I want to prove that there is one solution for e^z-z in every shifted copy of the fundamental strip by applying the argument principle to the boundary of a rectangle −M≤Rez≤M , 2kπi≤Imz≤2(k+1)πi for large M and integer k . I need help in using the...
  26. K

    Buoyancy Situation Doubt - Archimedes Principle

    Hi to all, i will appreciate your help in this. This is the situation: I have a tank, with a water column in it. This tank at the bottom has an "ideal" seal (a seal that permit the passing of object from bottom to upwards, but not the water to fall down.) In this system i have sphere with...
  27. I

    Electrostatics and the superposition principle.

    what is the whole concept of the superposition principle?
  28. D

    Equivalence Principle: Questions Explained

    Sorry for some probably very basic questions, but here goes. If gravity equals acceleration, how is the Earth's gravity defined by acceleration? If an accelerating body distorts spacetime, as described in Einstein's thought experiment about a light beam shined through an accelerating box...
  29. E

    Counting microstates in Boltzmanns principle

    Homework Statement Explain why the number of microstates W in Boltzmanns principle, is W = ƩNi! / ∏Ni! when i ideal gasses are mixed at constant volume and temperature. Ni is the number of particles of component i. Homework Equations S=klnW , where W is the number of microstates...
  30. L

    I need all the information about theHeisenberg's uncertainty principle

    I really can't understand the uncertainty principle,and now there are some experiment that violate the uncertianty principle, I need deepen understanding of quantum uncertainty,who can give me all the information about the uncertainty principle,such as new ideas,related study or books,thanks
  31. Astrum

    Static Equilibrium and D'Alembert's Principle

    Virtual work principle states: δW = \sum^{N}_{i=1}\vec{F}_{i}\centerdot δ\vec{r}_{i} And from this, we can see that if a system is to be in equilibrium we have δW = (\sum^{N}_{i=1}\vec{F}_{1} \centerdot \frac{\partial \vec{r}_{1}}{\partial q_{1}})δq_{1} + \cdots = 0 Where did q come...
  32. L

    Can the Holographic Principle Explain All Physical Information in a Surface?

    What is the reason/ explanation (possibly in a nutshell!) that all the physical information of a volume can be encoded in the surface surrounding that volume?Because, you know, that sounds silly, at first! I browsed some introductory sources, but could not find any quick answers. Also, if...
  33. S

    Question on Le Chatelier's principle

    When I have a reaction CO(g)+2H2(g) <=> CH3OH if I increas the concentration of CO, the equilibrium will be shifted to the right so more methanol will form. However, in that process won't the concentration of Hydrogen gas decrease? So won't that cause a change in equilibrium as well? If so, how...
  34. P

    Derivative using first principle definition

    Homework Statement Calculate the derivative of f(x) = x^3 - 3x^2 Homework Equations (f(x+h) - f(x))/h The Attempt at a Solution Just wondering if someone can check my solution. (f(x+h)- f(x))/h= ((x+h)^3- 3(x+h)^2- (x^3-3x^2))/h = (x^3+ 3x^2 h+3xh^2+ h^3-3(x^2+ 2xh+ h^2 )-...
  35. A

    Pigeonhole Principle and Boolean Matrices

    Homework Statement Let A be an 8x8 Boolean matrix. If the sum of A = 51, prove there is a row and a column such that when the total of the entries in the row and column are added, their sum is greater than 13. The Attempt at a Solution I considered a selection of one row and one column...
  36. K

    Principle of relativity hypothetical question

    Ok, so I have had a lot of spare time and started pondering the things of the universe. Mainly problems looking at time dilation, mass dilation, length dilation and gravity. So one day I came up with a question that I have been unable to answer and I wonder if it is answerable or if there are...
  37. nomadreid

    From statistical to ontological: uncertainty principle

    The derivation of the momentum/position Heisenberg Uncertainty Principle (HUP) is based on the statistical interpretation which says that if we have a lot of quantum systems in identical states, and measure the momentum in half of them and get a distribution with standard deviation σp, and...
  38. B

    Uncertainty principle regarding a narrow optical fibre?

    If we take a narrow aperture(such as the one used in the double slit experiments) and attach a length of optical fibre to it, surely now we know the position (confined by the width of the fibre) and also the momentum(defined by the direction of the fibre). How does the uncertainty principle...
  39. N

    Complex analysis proof with residue theorem, argument principle

    Homework Statement Let C be a regular curve enclosing the distinct points w1,..., wn and let p(w)= (w-w1)(w-w2)...(w-wn). Suppose that f(w) is analytic in a region that includes C. Show that P(z)= (1/2\pii)∫(f(w)\divp(w))\times((p(w)-p(z)\div(w-z))\timesdw is a polynomial of degree n-1...
  40. J

    Confused about the Equivalence Principle and Inertial Reference Frames

    Hey everyone, I started reading up on GR a couple of days ago, and I'm somewhat stuck on the concept of a free-falling IRF. I understand that an observer on a free-falling small spaceship would experience the laws of physics in a rather simple form, eliminating the need for a force of gravity...
  41. L

    The uncertainty principle and the measurement postulate

    Hi everybody. I have a quick question regarding the relationship between the uncertainty principle and the measurement postulate. According to the former, the higher our certainty is about the position of a particle, the lower our certainty is regarding its momentum, and vice versa. This...
  42. R

    Principle curvature: min and max curvature are always perpendicular?

    I am trying to understand Gaussian curvature. This led me into looking at principle curvature. Now If one takes a look at the picture of the "Saddle Surface" on Wikipedia here: http://en.wikipedia.org/wiki/Principal_curvature I see that at the point p on the saddle where curvature goes both...
  43. P

    Uncertainty principle using 2 detectors

    This may be a dumb question, but I am still new the the concept of the quantum world... If we can't measure position and momentum precisely at the same time, why can't we use 2 detectors? One to measure position, and one to measure momentum. Have them take the measurement at the same time, and...
  44. P

    Uncertanity Principle in Macrocosm

    A Macrocosm thing, example a car, can be exist two different places in the same time ?
  45. Q

    Estimating Atom Size using the Uncertainty Principle

    The typical energy needed to ionise an atom is around 5 eV. Use the Uncertainty principle to estimate the size of an atom. Homework Equations E=mc^2 E = p^2/2m Δx.Δp ≥ h/4π The Attempt at a Solution So I got the mass rearranging E = mc^2 m = 5*1.6*10^-19 / (3*10^8)^2...
  46. A

    Problem about uncertainty principle

    We have an electron pulse of width 1 nanosecond and with kinetic energy of 1keV. We have to calculate Δx and Δp. I have a question regarding this problem. If they give us the kinetic energy of the electron pulse then we know exactly the momentum right? And so the uncertainty of momentum would...
  47. C

    Heisenburgs Uncertainty Principle in a narrow tube?

    The principle states: δxδp≥h/4π I understand what it means and I've seen in proven both theoretically and expiamentally, so I am not questioning the inequality here. My question is: If there was a very narrow tube that had a vacuum inside it and a laser attached at one end that shoots...
  48. zrek

    Does Fermat's Principle Apply in All Special Cases of Light Path Alteration?

    Fermat's principle is the "path of least time principle" or we can say that "he path a light ray takes is a local minimum". Quantum physics also says that the light take (test) all possible paths and only the minimal remains. Is it working in special cases like this too? Let's examine the fig...
  49. E

    Simplified Carburettor (Venturi Principle) Problem

    Homework Statement A carburettor in a petrol engine works on a Venturi principle as sketched below. The pressure difference across the contraction draws fuel up from the reservoir and ejects it through a circular cross-section pipe into the main airstream, where it mixes with air. A...
  50. F

    Examples of progress due to the Copernican Principle?

    Heliocentrism is a main example of how a physical law changed due to the Copernican Principle - that is, that we as humans on the Earth are not privileged or special in the universe. Are there many other examples from the history of science where a major advance in the development of a...
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