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. B

    I Proving Torricelli's Law Using Bernoulli's Principle

    There is a standard proof of this kind in which two points are taken - one at the top of the water and one just outside the spout or opening. I guess my question kind of assumes that you've seen something like this. A key step of the proof is to say that the difference of pressures, perhaps...
  2. T

    Superposition Principle for two Voltage Sources (confusions about....)

    I have a question about natural limitations when the superposition principle for circuits is applicable. Possibly there is a quite elementary reason why the problem I'm going to present next fails, but up to now I haven't a precise reason why that's exactly the case. Could somebody help...
  3. M

    I Heisenberg Uncertainty Principle Violation?

    Hello, 2 questions please about the Uncertainty Principle and the following scenario: I shoot at each other, 2 electrons each with equal but opposite velocity such that they repel each other? (To me, this indicates that you know the momentum of each electron and you know each position...
  4. Huzaifa

    Chemistry Effect of temperature change in Le Chatelier's Principle

    The effect of temperature change in Le Chatelier's Principle is given by the equation $$ \log \left(\frac{\mathrm{K}_{2}}{\mathrm{~K}_{1}}\right)=\frac{\Delta \mathrm{H}}{2.303 \mathrm{R}}\left[\frac{1}{\mathrm{~T}_{1}}-\frac{1}{\mathrm{~T}_{2}}\right] $$. How to derive $$ \log...
  5. DaTario

    I A proof of Archimedes' Principle

    Hi All, is there a proof to Arquimedes Principle and the expression for the buoyancy force? In case there is a proof, may we refer to this as Arquimedes theorem? (Buoyancy force = density of the fluid x acceleration of gravity x submerged volume) Best Regards, DaTario
  6. PhilipsPhysics

    I Where does Hamilton's Principle come from?

    Hamiltons Principle and the physcial entity action are the terms in which modern physics is formulated. How do you know that you can always find a Lagrangian for a System which is then used for Hamitlons Principle and the formulation of Action? Why is the action stationary?
  7. S

    I Anthropic Principle: Exploring Logical Explanations

    And was confused on the implications. Is there a more logical explanation for this? I'm very confused on what's happening here
  8. 1

    Using Variational Principle to solve ground state energy

    First I picked an arbitrary state ##|ϕ⟩=C_1|φ_1⟩+C_2|φ_2⟩+C_3|φ_3⟩## and went to use equation 1. Realizing my answer was a mess of constants and not getting me closer to a ground state energy, I abandoned that approach and went with equation two. I proceeded to calculate the following matrix...
  9. only1god

    I What if Einstein equivalence principle is proven wrong one day?

    What would be the consequences of such thing? How it will affect physics theories and the world?
  10. L

    I Fermi Gas Model: Energetic Degeneration & the Pauli Exclusion Principle

    In the fermi gas model, there is assumption that there is a 3D potential well, but there is "energetic degeneration" for each three index "nx, ny, nz". Now the problem is with that image, if there is degeration, for some level En there may be 10 distinctive state with same energy, so there is 20...
  11. P

    Find R.H. Dicke's Paper: "Gravitation without a Principle of Equivalence

    Summary:: Searching for Paper by R H Dicke Good day all. Does anyone know where I might obtain a copy of the Paper R. H. Dicke. Gravitation without a principle of equivalence. Review of Modern Physics, 29(3):363–376, 1957 I am prepared to pay for it. Thanks Paul
  12. Jim Kata

    I Participatory Anthropic Principle

    Consider the following thought experiment, two electrons are in an entangled state with a total angular momentum of zero. They split apart from each other some billion or so years ago and I observe one of the electrons right now. Before the observation, there is some probability that it will be...
  13. Dario56

    I Work - Energy Principle Application to Fluid Flow

    In classical and continuum mechanics if we want to find equation of motion of the body we draw force diagram and apply Newton's 2nd law. In continuum mechanics, equation of motion actually refers to a special point of the body known as center of mass (COM) which can be proven by definition of...
  14. Dario56

    I Work - Energy Principle Application to Fluid Flow

    Work - energy principle states that work done by net force acting on the body equals change in kinetic energy of the body. We are talking about continuum mechanics. This principle is usually introduced in mechanics of solid bodies. For us to describe the motion of the body, it is enough to know...
  15. Dario56

    I Bernoull's Equation Derivation From Work - Energy Principle

    Work - Energy principle states that work of resultant force or sum of work of all forces acting on some system equals change in kinetic energy of the system. For inviscid fluid flowing in a pipe such theorem can be used to derive Bernoulli's equation because as fluid flows it is subjected to...
  16. S

    A Is the self-consistency principle a scientific or philosophical idea?

    As I understand it, the Novikov's principle is either philosophical or scientific. I heard that it is a consequence of the stationary-action principle (principle of least action) in quantum mechanics. Does this mean that Novikov's principle is scientific? I also heard the following: in quantum...
  17. S

    B Equivalence Principle and Rindler Horizons

    I just thought of this. I'm not an expert, so cut me some slack if I get something wrong. Given: 1) Acceleration is supposed to produce a Rindler horizon. 2) If I understand it correctly, under Relativity and/or the Equivalence Principle, standing on (for example) the Earth is the same as...
  18. T

    Dynamics of Four Bar Link using Hamilton's Principle with Loop Closure

    Summary:: Can someone point me to an example solution? Hello The attached figure is a four bar link. Each of the four bars has geometry, mass, moment of inertia, etc. A torque motor drives the first link. I am looking for an example (a simple solution so I can ground my self before...
  19. elcaro

    I Cosmological principle about space and time

    AFAIK there is no cosmological principle formulated about space and time. If it would be formulated, it would more or less state that spacetime is an interconnected whole, and has no gaps, edges or boundaries. It doesn't need to state wether spacetime is finite or infinite, that is an open...
  20. K

    A When is Hamilton's principle valid?

    When is Hamilton's principle##\delta \int L d t=0## valid ? Is it only valid for monogenic and holonomic systems? What about monogenic and non holonomic systems? (I'm asking this because I got confused because I've found that Goldstein has got something wrong related to this in his 3rd edition)
  21. K

    A Hamilton's principle and virtual work by constraint forces

    Found a question on another website, I have the exact same question. Please help me Goldstein says : I do not understand how (2.34) shows that the virtual work done by forces of constraint is zero. How does the fact that "the same Hamilton's principle holds for both holonomic and...
  22. S

    I Feynman's Vol 1 Lecture 26 Principle of Least Time (help with Figure)

    Hello, Just for fun - I am trying to go through The Feynman’s Lectures: Lecture #26 – Volume 1: The Principle Of Least Time. I am stuck on Figure 26-4 and specifically showing the two angles with the “double arcs” are equal. The angle of reflection BCN’ and XCF. Maybe I am just that rusty on...
  23. T

    A Exploring Why Hamilton's Principle Uses L=KE-PE Lagrangian

    As I understand, Hamilton's Principle with the L = KE - PE Lagrangian, leads to Newton's equation. Why MINUS and not PLUS? I have seen many attempts at such a proof and I now realize that one does not prove PRINCIPLES. Like Laws, they are observations. It produces an equation that describes...
  24. P

    I Violation of Special Relativity Principle?

    From the michelson-morley experiment, if a clock were to measure the time period of light hitting the mirror and returning back, it would be 2L/c, where L is the distance between the laser nd the mirror. For a moving observer, the time period would have a factor of *gamma*, the boost factor...
  25. Ebi Rogha

    I Uncertainty principle equation for virtual particles

  26. S

    I Does the CMB reference frame violate the Cosmological Principle?

    Studies of the Cosmic Microwave Background shows that the Earth is moving roughly 380 km/s with respect to it towards the constellation Leo I think. Yet (I think) the Cosmological Principle and the Michelson-Morely experiments suggest there is no preferred reference frame in the universe --...
  27. cianfa72

    I Principle of relativity for proper accelerating frame of reference

    Hi, I've a doubt about the application of the principle of relativity as follows. Assume as principle of relativity the following statement: It is impossible by any experiment performed inside a "closed" laboratory to say whether we are moving at constant velocity or staying at rest. Consider...
  28. S

    MHB Work energy principle and power

    Particle X of mass 2 kg , and particle Y of mass m kg are attached to the ends of a light inextensible string of length 4.8m. The string passes over a fixed smooth pulley and hangs vertically either side of the pulley. Particle X is held at ground level, 3m below the pulley. Particle X is...
  29. S

    MHB Work energy principle and power

    A car of mass 1200 kg accelerates up a hill inclined at 10 degree to the horizontal. The car has initial speed of 10 m/ s and final speed of 12 m/s after 60 s. Air resistance and friction may be ignored. Find the average power generated by the engine. The and in the textbook is 36000 W, iam...
  30. S

    MHB Work energy principle and power

    A golf ball of mass 45.9g is hit from a tee with speed 180km/ h. The ball rises to a height of 20m having traveled along a curved path of length 61.875m. At the highest point of its path the ball is traveling at 144 km/h a) Find the magnitude of the avg resistance force acting on the golf ball...
  31. M

    I Equivalence principle question

    The equivalence principle states that a person stood on Earth would experience “gravity” the same as if he was in an elevator in space traveling at 1g. I get this. but when Einstein was first exploring this, I read he came to the realisation that a person free falling on Earth (if in a vacuum)...
  32. S

    MHB Work energy principle and power

    A golf ball of mass 45.9g is hit from a tee with speed 50 m/ s. The ball lands in a pond 5m lower than the tee. When the ball lands in the pond it has traveled a curved path of length 160m. The resistance acting on the ball has magnitude 0.3N a) Find the speed of the ball just before it hits the...
  33. S

    MHB Work energy principle and power

    A sky diver of mass 80 kg falls 1000m from rest and then opens his parachute for the remaining 2000m of his fall. Air resistance is negligible until the parachute opens. The sky diver is traveling at 5 m/ s just before he hits the ground. Find the average resistance force when the sky diver is...
  34. S

    MHB Work energy principle and power

    A football is kicked from the ground level with speed 15m/s and rises to a height of 1.45m. Assume that air resistance is negligible a) Find the speed of the ball when it is 1m above the ground Increase in GPE= loss of KE mgh=1/2mu^2-1/2mv2 10×(1.45-1)= 1/2×15^2-v^2/2 V= 14.7 m/ s But textbook...
  35. S

    MHB Work energy principle and power

    A box slides down a smooth ramp. The height of the ramp is 20cm and the length of the ramp is 2.5m. The box starts from rest. What is the speed of the box when it reaches the bottom of the ramp? I don't understand how to solve this. Pls help
  36. S

    MHB Work energy principle and power

    A child of mass 40kg slides down a playground slide. The child starts from rest at the top of the slide, 2m above the ground. At the bottom of the slide it's slope levels off. a) Find the child's loss of GPE I got the ans 800J there is a constant resistance of 112N throughout b) find the...
  37. S

    MHB Work energy principle and power

    A girl of mass 50 kg travels down a water slide. She starts at the top with a speed of 2 m/s and descends through a vertical height of 5m. a) Assuming that there is no resistance, find her speed when she reaches the bottom of the slide I got the ans 10.2m/ s b) the girl's actual final speed is...
  38. S

    MHB The work energy principle and power

    A box of mass 25kg is pulled 5m across a smooth floor by rope with tension 22N. The rope is inclined at 40 degree to above the horizontal. There is a frictional force with average value 12N. The box starts from rest. Find the final speed. Iam getting the ans 1.97m/s. The textbook ans is 1.39 m/s...
  39. Paige_Turner

    B Okay, so is Mach's principle true, or not?

    You don't need another object in the universe in order to rotate and feel centrifugal force. You establish an inertial frame just by sitting there and existing. When you rotate, you rotate relative to that frame, even though the only mass in it is rotating. Or am I, like, WAY off? If so...
  40. lemma28

    B Fermat's principle and refraction -- Possible misunderstanding

    Consider a light starting at A in media 1 and going in and out a media 2 (say shaped as a disk) with relative index of refraction n to arrive at point B (in media 1). Fermat's principle says that the path taken by the ray between points A and B is the path that can be traversed in the least...
  41. L

    I D'Alembert's principle vs Hamilton's principle

    In the first two chapters of Goldstein mechanics, the Lagrange equations are derived from both D'Alembert's principle and Hamilton's principle. I want to know what're the applicability of these two approaches to Lagrangian mechanics? Is one more powerful than the other or are they completely...
  42. Delta2

    I Can the Principle of Least Action Unify Different Branches of Physics?

    From what I know Newton's 2nd law in classical mechanics can be derived from the principle of least action. Also from what I know, two of the Maxwell's equations (those that contain the time derivatives, i.e. Maxwell-Faraday law and Maxwell-Ampere law) also can be derived from the principle of...
  43. DaalChawal

    MHB Number of principle solutions of the equation

    Find number of principal solutions of the equation $sinx + cosx + sin2x + cos2x + sin3x = -1 $ Please help anyone wihout using desmos
  44. H

    Can I use the principle of conservation of energy for this problem?

    ddd
  45. UFSJ

    A Magnetic exchange interaction by first principle (Blume-Capel model)

    Hi guys. I work with statistichal mechanics, applying classical spin models, as Ising model. I'm trying a collaboration with a colleague that works with first principle calculations. Does anyone know how to calculate the exchange interaction and anisotropic constant (of the Blume-Capel model)...
  46. B

    MHB Physics - Archimedes principle

    Im having trouble with the following question regarding Archimedes principle. A wooden board with an area of 4.55m^2 is dropped into the dead sea (P sea- 1240 kg/m^-3). Calculate the proportion that would float above the surface. (P wood - 812 kg/m^-3). My understanding is that the volume (V...
  47. L

    B Simple reasoning that the equivalence principle suggests curvature

    I am a high-school teacher and a PhD. student. I am looking for ways to introduce my students to GR. In my treatment, I speak about the equivalence principle and later about curvature in general and consequently that of spacetime. I am missing a connection of these two parts that would be...
  48. B

    4 Pole Induction Motor Working Principle

    Hello, I am studying the working principle of an induction motor. The attachment below (link) is a portion from Stephen J. Chapman's textbook (page 160-169). He proved the theory of the rotating magnetic field so well for a 2-pole induction motor from 160 to 164. However, on page 166, the...
  49. C

    Technique for proving Inclusion-Exclusion principle combinatorically

    This is a popular combinatorial proof for the Inclusion-Exclusion principle but I was wondering what kind of proof technique they use? Initially I thought - since we have cardinalities on both sides of the equality , I thought we'd have to show a bijection exists between the set on the left...
  50. AdvaitDhingra

    B Question regarding the equivalence principle

    Hello, So I read that a person in a rocket accelerating at 9.8m/s^2 would feel the same pull downwards as a person standing on the Earth's surface. However, I can think of a few instances where you could tell the difference: - If you measure g (9.8N/kg) on Earth, you will notice that the...
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