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. adsorption

    I Anyone knows V-Sorb 2800 BET surface area analyzer principle

    we interest one V-Sorb 2800 BET surface area analyzer, using physical adsorption principle to test particles surface area data, if anyone knows this analyzer principle?
  2. P

    Archimedes Principle: Pure gold or not?

    Homework Statement Archimedes, prove your stuff. A royal crown (cola?) of pure gold is suspended in air by a thread and the tension in the thread is of magnitude T. When the crown is totally immersed in water, the magnitude of the tension in the thread is 0.872T. A) sketch a second law force...
  3. huffy

    Archemides principle/ Center of buoyancy

    Homework Statement One way of moving a large undersea rock or mooring is to fasten a closed, empty oil drum to the rock while at low tide. As the tide comes in the drum is drawn down into the water increasing the buoyant foce acting on the system of the rock and drum. Suppose a cylindrical drum...
  4. Physics Dad

    Archimedes's Principle Question

    Hi, I have an issue with a question I am trying to answer and I don't seem to be getting the correct answer... Question A 950kg cylindrical can buoy floats vertically in sea water, the diameter of the buoy is 0.860m. Calculate the additional distance the buoy will sink when a 70kg man stands...
  5. N

    I Church-Turing-Deutsch principle and Incompleteness-Halting.

    The Church-Turing-Deutsch Principle states that any physical law can be computed. This is a strong statement which many physicists assume without justification to be true at face value. However, I have not seen proof of the CTD principle being true. From what I understand David Deutsch...
  6. N

    I Proving The Church-Turing-Deutsch Principle

    How does one prove the Church-Turing-Deutsch Principle? The principle states that a universal computing device can simulate every physical process. Not sure where to post this, as it seems like a pertinent question in proving the simulated universe thesis right or wrong along with possible...
  7. A

    Fluid Mechanics and Archimedes Principle

    Homework Statement [/B] A rectangular object has a width of 40 meters, height of 15 meters, and length of 2 meters. It floats consistently when 3 meters of its height is below the surface of the water. 1. Find the volume of the displaced water. 2. How much is the buoyant force on the object...
  8. B

    I How can the Equivalence Principle hold when we consider tidal forces?

    Tidal Forces: "It arises because the gravitational force exerted by one body on another is not constant across it". which implicitly implies that the acceleration is not constant on that body. Equivalence Principle: "weightlessness sensation occurs when one free falls in gravity" - which...
  9. H

    I What is the reason behind fermions being unable to share the same quantum state?

    What is the explanation for the case that fermion's can't occupy the same quantum state? Is there some logic behind this or is it just observation?
  10. B

    B Uncertainty Principle and a photon

    Let a photon of a definite wavelength (hence a definite momentum ) start it's journey at time 0. After 8.3 minutes it hits a detector on earth. So it's position is exactly known (in fact it can be predicted for any time less than 8.3 minutes). So we have particle with definitely known momentum...
  11. evinda

    MHB Maximum principle for subharmonic functions

    Hello! (Wave) I have a question about the proof of the maximum principle for subharmonic functions. The maximum principle is the following: The subharmonic in $\Omega$ function $v$ does not achieve its maximum at the inner points of $\Omega$ if it is not constant. Proof: We suppose that at...
  12. Kara386

    I Uncertainty Principle: Energy of Unstable Particle?

    For an unstable particle is it reasonable to take the uncertainty in energy as the energy it was created with? If so, why?
  13. Ryan Hardt

    Uncertainty in Wavelength Calculation from Wave Crests on a Pier

    Homework Statement Standing in the middle of a 20 m long pier, you notice that at any given instant there are 15 wave crests between the two ends of the pier. Estimate the minimum uncertainty in the wavelength that could be computed from this information. Homework Equations [/B] Uncertainty...
  14. Hamal_Arietis

    What Does Over Time Imply in the Context of the Huygens–Fresnel Principle?

    Homework Statement I don't understand about some words of this problem. Does "over time" mean? Why constructive interference (CI) appear? Homework Equations I think we use The Huygens–Fresnel principle The Attempt at a Solution I choose answer 3-c But I don't know the physical phenomenon.
  15. dccd286

    B Does the Uncertainty Principle work through barriers?

    I'm currently designing an experiment on Double slits for a high school science fair, but I'm not sure whether it's plausible or not. I'll be spending some of my savings for this, that's why I would like to hear some feedback from more-knowledgeable people first. In this experiment, I am trying...
  16. DoobleD

    B Proof / derivation of d'Alembert principle?

    I can't find a derivation of d'Alembert principle. Wikipédia says there is no general proof of it. Same with stackexchange. I find it surprising so I thought I'd come here to check with you guys. D'Alembert principle has indeed no proof ?
  17. A

    How Does Huygen's Principle Explain Wave Propagation?

    Homework Statement Homework Equations N/A The Attempt at a Solution [/B] Okay, it is not an assignment question. I am just looking for an explanation regarding something I read. Why is the diagonal distance travel time(^-1) equal to (n_2 - n_1){(\frac{1}{c_1} + \frac{1}{c_2})} ?
  18. C

    Understanding Leveling Procedures for Benchmark and Temporary Benchmark Points

    Homework Statement is it a must that that the levelling work must commence and ends at benchmark or temporary benchmark of known point ? Homework EquationsThe Attempt at a Solution I think not , because we can commence the levelling work at a point of known elevation ( benchmark / temporary...
  19. A

    I Huygen's principle in practical sense

    Hello everyone, I have two little clarifications to make about Huygen's principle: - Why doesn't the wave go backward? I mean, if every point on the plane acts as the source of a secondary wavelet, then, along with the envelop which makes the wave travel apparently forward, another should...
  20. M

    I Sum principle proof: discrete mathematics

    Theorem: Let ##A_1, A_2, ..., A_k## be finite, disjunct sets. Then ##|A_1 \cup A_2 \cup \dots \cup A_k| = |A_1| + |A_2| + \dots + |A_k|## I will give the proof my book provides, I don't understand several parts of it. Proof: We have bijections ##f_i: [n_i] \rightarrow A_i## for ##i \in [k]##...
  21. FallenApple

    A Gravitational Redshift in Newtonian Equivalence Principle?

    So I was reading that the equivalence principle of Newton doesn't work because of a thought experiment. They said that an experimenter shoots bullets( 1 per second) from the bottom of the elevator to the top. This happens in outerspace where the elevator moves up with accleration g. And this...
  22. S

    I Schroedinger Equation from Variational Principle

    Landau's nonrelativistic quantum mechanics has a "derivation" of Schroedinger's equation using what he calls "the variational principle". Apparently such a principle implies that: $$\delta \int \psi^{\ast} (\hat{H} - E) \psi dq = 0$$ From here I can see that varying ##\psi## and...
  23. DaTario

    I Pascal´s Principle in Compresssible Fluids

    Hi All, When explaining Pascal´s Principle I had some bad time related to its application in compressible fluids. Correlation functions (forces in two points separated in space at the same time) came to my mind but at the end the doubt persists. Is Pascal´s Principle valid for compressible...
  24. T

    Centripetal Force and Pascal's Principle

    I am trying to reconcile what I understand about Pascals Law in Fluid Statics and Centripetal Force in Fluid Dynamics In fluid statics pressure always acts normal to the wall . The explanation I have seen https://www.physicsforums.com/threads/fluid-mechanics-and-perpendicular-force.733437/ Is...
  25. P

    I Is Fermat’s principle appicable to a plane wave?

    Fermat’s principle states that light follows the path of least time. In textbooks, a specific formulation of Fermat’s principle is about the optical path between two points, A and B: How can a ray of light, emitted from point A, reach point B? Suppose that there is a plane wave in free space...
  26. eow

    I Are Superposition, the Uncertainty Principle, and Duality the same?

    Are quantum superposition, Heisenberg uncertainty principle, wave/particle duality the same thing? Do they imply each other? They all seem the same to me like the wave-like nature of photons -> superposition, and superposition means there's not definite position -> uncertainty principle. Sorry...
  27. P

    Some questions about Steam Injector principle

    http://www.mekanizmalar.com/how-steam-injectors-work.html In the link above, the basics of steam injector is given. Steam Injector's don't have any moving parts and doesn't consume any energy by themselves. Still, it can be able to pressurise water and inject that to a high pressure Boiler by...
  28. victorhugo

    I What causes Heisenberg's uncertainty principle?

    I know the equation which explains how it works, but why is it like that? The closest thing I can think as to why is because of the wave-particle duality of matter given by λ=h/mv, which also explains itself. But I don't know exactly why.
  29. F

    Is My Professor Wrong? Understanding the Work-Energy Principle

    See attached file. I believe my professor is incorrect. Work in must equal work out. We can imagine the work done by the mass as being a separate issue. Then, we recognize that the work done by the spring must be the same. Am I right? If not, why?
  30. H

    B Uncertainty Principle - uncertainty in mass.

    Physicists often speak of the uncertainty principle in terms of position and velocity (in momentum). But momentum is Mass X Velocity. Why is it that we can say something like "a particle with a well defined position has high uncertainty in velocity". But I never hear a statement like "a particle...
  31. Deebu R

    B Archimedes Principle: Weight of Immersed Object

    I was just a bit confused about Archimedes principle. Say an object is partially immersed in water. The weight of water water displaced will be equal to weight of the entire object or just the part immersed in water?
  32. certainice

    Energy principle example problem in classical mechanics book

    Homework Statement A man of mass 100 kg can pull on a rope with a maximum force equal to two fifths of his own weight. [Take g = 10 ms^2] In a competition, he must pull a block of mass 1600 kg across a smooth horizontal floor, the block being initially at rest. He is able to apply his maximum...
  33. majormuss

    I Understanding the Uncertainty Principle

    Hi everybody, I was reading about the Uncertainty principle and I came across the statement: "the position-space wavefunction of a minimum-uncertainty state is a Gaussian. Indeed, because it’s a minimum-uncertainty state, its momentum-space wavefunction is also a Gaussian."...
  34. A

    A Exploring the Pauli Exclusion Principle and Black Holes

    The event horizon of a black hole appears to be plastered with 'afterimages' of everything that ever fell into it. (Because gravitational time dilation makes every such object appear to stop at the event horizon.) Now, suppose an event horizon is 'full' as defined by the Pauli exclusion...
  35. P

    A Exploring Huygens' Principle: Odd # Spatial Dimensions & Beyond

    A spin-off from another thread. I consulted a couple of my GR textbooks on Huygens' principle, and found little. Wiki had a little information, which said that it could be regarded as a consequence of the homogeneity of space-time, and "In 1900, Jacques Hadamard observed that Huygens'...
  36. e2m2a

    A Einstein, Mach's Principle, and the Speed of Light Limit

    I am confused about Einstein's thinking. I understand when he formulated his general theory of relativity, he wanted to incorporate 3 foundations for his theory: The relativity principle, the equivalence principle, and Mach's Principle. He believed that inertia and weight were essentially the...
  37. haushofer

    Hamilton's principle and minimum potential energy

    Dear all, I was wondering what exactly the correspondence/relation is between Hamilton's principle (extremizing the action gives the allowed configurations) and the fact that a system wants to configurate such as to minimize its potential energy. Is there any? Somehow I can't find a decent...
  38. C

    B Heisenberg's uncertainty principle and photons

    Hi everyone, Apologies if this is common knowledge or a silly question, I'm just coming back to physics and I've been looking through the double slit experiments ( both double slit and delayed choice quantum eraser ) and it got me thinking about the uncertainty principle. With a photon of...
  39. T

    Archimede's Principle to Make a Cup Float to Certain Height

    Homework Statement I am given a water tank, a small plastic cup, and some gravel. How could I use Archimede's principle to determine how much gravel to put in the plastic cup such that it sinks to a certain point (namely the rim), but then floats, so that no water is let inside the cup...
  40. Chris Frisella

    B Help Understanding the Uncertainty Principle

    To check my understanding, imagine this scenario: You have a very small surface rigged as a light detector (the contact surface is let's say a single atom). You then fire off single photons towards it. As soon as you get a read on the detector, you know very precisely where the light is/was, and...
  41. C

    I Heisenberg Uncertainty Principle

    Hi all, I am 18 years old, and am looking to go into engineering, but I have a strong interest in theoretical physics. As such I have recently written a short research paper into the Heisenberg Uncertainty Principle, and I wondered if anyone would be willing to have a quick read and give me any...
  42. J

    I About the Equivalence Principle

    Hey all, I was trying to compare the similarity between time dilation due to gravity and the scenario of an accelerating rocket through the equivalence principle and there's something tha blocks my understanding about their similarity. I found a good distance-time graph of the accelerating...
  43. G

    I Classical/QM justification of principle of least action

    Hi. Is the principle of least (better: stationary) action only an axiom in classical mechanics, or can it be derived from a more profound (classical) principle? As far as I know, it can be derived from the path integral formulation of QM. Is this a more profound justification for the principle...
  44. WCOLtd

    B Mach's Principle: Understanding the Universe's Rotation Around Us

    How come when I spin around, the universe doesn't fly apart as if its rotating around me? Why is my frame of reference that I am at rest and its the universe spinning around me not valid?
  45. LLT71

    I Fermat's principle of least time

    while I was studying "fermat's principle of least time" I was (and still I am) ntrigued by the fact that "out of all possible paths that it might take to get from one point to another, light takes the path which requires the shortest time". this question may be a bit philosophical but: "how"...
  46. Y

    B An application of the uncertainty principle

    It is in the IB textbook. Said as an application of the uncertainty principle, consider an electron, which is known to be confined in a region of size L. We know the uncertainty in position of the electron must satisfy Δx<L. Therefore, according to the uncertainty principle, we can work out...
  47. J

    I Something about Archimedes' Principle

    Hello, I was reading about Archimedes' Principle on the wiki ( https://en.wikipedia.org/wiki/Archimedes%27_principle ) and a question popped up regarding the upthrusting force (also called buoyant force) that the liquid exerts on an object that is in the liquid. I understand that the...
  48. weezy

    I What is the reason behind uncertainty principle?

    Heisenberg's uncertainty principle: due to experimental limitations or dual nature of matter? Or both?
  49. rezkyputra

    Deriving Einstein Eq. from Variational Principle

    Homework Statement Okay, in Carrol's Intro to Spacetime and Geometry, Chapter 4, Eq. 4.63 to 4.65 require a derivation of a difference between Christoffel Symbol. I did the calculation and found my answer to be somewhat correct in form, but the indices doesn't match up Homework Equations So...
  50. Madi Araly

    I Uncertainty Principle.... Intent Behind It?

    I've been pre-occupied with Heisenberg's uncertainty principle for around four years now, and I've come to fabricate a lot of questions. The most pressing one, however, is as follows: To me, the uncertainty principle seems to reference our (relatively) poorly controlled methods to measure a...
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