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. F

    B SONAR: Echo vs Reflection of Sound Waves

    When asked what the principle of SONAR is, is writing 'echo of sound waves' less accurate than 'reflection of sound waves'? They basically are the same...
  2. Hiero

    I Theorem behind Archimedes principle of buoyancy?

    I was thinking about why the buoyant force on an object should depend solely on it's volume and not shape. It seems loosely like the divergence theorem in that an integral over the surface is determined by the volume. There is a big difference though; in the divergence theorem we integrate...
  3. C

    Virtual work and D'alembert's principle

    I can't for the life of me figure out what virtual work or D'alemberts principle mean and what the intuition behind them is. As far as I'm concerned D'alemberts principle is just a restatement of Newton's second law but considering the work instead of just the forces. What am I missing? I'm...
  4. LarryS

    I Is Entropic Uncertainty Principle taken seriously in QM?

    Is the Entropic Uncertainty Principle taken seriously by experimental physicists? For example, is it considered more accurate than the HUP that uses standard deviations? Thanks in advance.
  5. Math Amateur

    MHB The Well-Ordering Principle for the Natural Numbers

    I am reading Ethan D. Bloch's book: The Real Numbers and Real Analysis ... I am currently focused on Chapter 1: Construction of the Real Numbers ... I need help/clarification with an aspect of Theorem 1.2.10 ... Theorem 1.2.10 reads as follows: Towards the end (second last line) of the...
  6. Math Amateur

    I The Well-Ordering Principle for the Natural Numbers ....

    I am reading Ethan D. Bloch's book: The Real Numbers and Real Analysis ... I am currently focused on Chapter 1: Construction of the Real Numbers ... I need help/clarification with an aspect of Theorem 1.2.10 ... Theorem 1.2.10 reads as follows: Towards the end (second last line) of the...
  7. FallenApple

    A Argument for Holographic Principle

    So around 44:00, Susskind begins his argument. He put a variety of items into a region of space, and the added a minimal shell of material surrounding the items, then squeezed that material to form a black hole around the item. Then he said that the amount of original information cannot be...
  8. EEristavi

    How does a 5th wheel contribute to the accuracy of car speedometers?

    I'm wondering how does speedometer work. To be specific let's talk about car speedometer. I googled it and found out that there are different kind of speedometers, but not quite understood it's working principle. My question is not about how it shows us speed (Mechanically with arrow or...
  9. M

    Discrete LQR regulator and Bellman's principle

    Hello everyone. Iam studying the LQR regulator in optimal control theory right now but Iam having some issues in understanding the approach of Bellmans principle. As far as I have understood, in Bellmans dynamical programming approach, one goes backward in time to find the optimal Gains K...
  10. Thejas15101998

    I Forms of the Uncertainty Principle

    Well, i came across the so-called both the forms of the uncertainty principle of Quantum Mechanics: the position-momentum form and the energy-time form; but i am not satisfied in one way. Here the trio: position, momentum and energy, all of them have their own operators, but time does not have...
  11. C

    B Shape of Universe & Cosmological Principle

    Let me preface this post by saying that I only have a very cursory understanding of general relativity. I happen to know that if we assume the cosmological principle, then the hypersurface ##\Sigma_t## of the spacetime manifold ##M##, for any positive ##t##, is either a 3-sphere, a...
  12. Pushoam

    I Is the Principle of Relativity different for different theories?

    The images have been taken from the section : Relativity according to Galileo and Newton, page no.66, special relativity , A.P.French,1968What I understood is: According to the first paragraph, Laws of transformation are needed so that a theory which describes a phenomenon w.r.t. one reference...
  13. J

    Classical mechanics: Jacobi variational principle

    An isolated mechanical system can be represented by a point in a high-dimensional configuration space. This point evolves along a line. The variational principle of Jacobi says that, among many imagined trajectories between two points, only the SHORTEST is real and is associated with situations...
  14. T

    B Is Inertia Tied to the Stars According to Mach's Principle?

    Mach, Newton and others observed that centrifugal forces appear in a object when it rotates in relation to the stars. Einstein was convinced by this and tried, unsuccessfully as far as I understand, to incorporate what he called Mach’s Principle into General Relativity. From Wikipedia -”Mach’s...
  15. Lunct

    I What are the units for the Heisenberg Uncertainty Principle?

    To my understanding(correct me if I am wrong), one consequence of the Heisenberg Uncertainty Principle is that energy levels can fluctuate by some amount, e, for a short time, t. As long as e x t does not exceed h/4pi (where h= Planck's constant). My quarry is that what are the units for the...
  16. vktsn0303

    A Understand Convolution, Singularity, Kernel, etc: Math Reading Guide

    I'm reading a book on vortex methods and I came across the above mentioned terms, however, I don't understand what they mean in mathematical terms. The book seems to be quite valuable with its content and therefore I would like to understand what the author is trying to say using the above...
  17. yecko

    Chemistry: First principle of thermodynamics

    Homework Statement https://holland.pk/uptow/i4/1ca04ddf7c25f6c63e307720c34a4ff3.png Homework Equations First principle of thermodynamics: E=q+w The Attempt at a Solution E=q+w=-17+21=4kJ>0 ∴Endothermic (absorb heat from surrounding) (a) false (from surrounding to the system) (b) false (does...
  18. Mr Real

    I Intuition behind elementary operations on matrices

    For finding the inverse of a matrix A, we convert the expression A = I A (where I is identity matrix), such that we get I = B A ( here B is inverse of matrix A) by employing elementary row or column operations. But why do these operations work? Why does changing elements of a complete row by...
  19. C

    What is a good film that has examples of the Bernoulli Principle

    We have to find a movie that has 3 good examples and 3 bad examples of this principle. We were thinking about doing Finding Nemo however we can't think of 3 bad ones and we are worried that our physics teacher might reject it since it is not a "serious" movie. Any ideas?
  20. N

    Exploring Archimedes Principle: A Step-by-Step Demonstration

    Homework Statement Hi, in my high school physics class we have to teach (part of) a lesson, mine being archimedes principle, and we have to make a demonstration of our topic. My idea was to show how you can calculate the buoyant force on a immersed object with the weight of the water it...
  21. M

    MHB What is the principle when borrowing $3100 at 15% per three years?

    When Dave borrowed $3100 at 15% per three years, the principle was? Do I use I = prt? If so, the set up is 3100 = p(0.15)(3), right?
  22. Sanchayan Ghosh

    The principle and mathematics behind Klein's construction?

    Hello, I tried looking this up a lot and just could not find it. For four bar linkage, Klein's construction is used to find velocity and acceleration of piston and connecting rod. Here is a link for the procedure of the same...
  23. P

    I Weak Maximum Principle Explained

    Hello,I am reading the link http://math.mit.edu/~jspeck/18.152_Fall2011/Lecture%20notes/18152%20lecture%20notes%20-%204.pdfSays : w_t-D w_{xx}=f with f<0w at \bar{Q}_T has its maximum in \partial_p {Q}_T. If w is strictly negative at \partial_p {Q}_T then also is strictly negative in...
  24. Y

    MHB How Can the Pigeonhole Principle Solve These Mathematical Puzzles?

    Hello all, I have a few small questions, related to the pigeonhole principle, which should be the guiding line for the solution. I had more, but solved the easier ones. 1) Prove that each series of 10 integer numbers has a sub-series of following numbers such that the sum of the sub-series is...
  25. Buzz Bloom

    I Is the Holographic Principle the Key to Understanding Our Universe?

    I have just come across the following on the Astronomy Picture of the Day. https://apod.nasa.gov/apod/ap170423.html Here is a quote that I would like to learn more about. The Holographic Principle, yet unproven, states that there is a maximum amount of information content held by regions...
  26. S

    Finding magnitude and direction of reaction force

    Homework Statement A uniform horizontal rod of mass 4 kg and length 500 mm, is hinged at the left hand side and supported at rest by a chain (S) attached 10 cm from the hinge. Calculate the magnitude and direction of the reaction force on the rod at the hinge. State the principle you have...
  27. goatz4real

    Find velocity of air using Bernoulli principle

    Homework Statement A horizontal stream of air is blown just above the open end of the hares apparatus with an initial speed "V". The density of air is 1.2 kgm-3.Then the water column rises to 6 cm in the respective limb.Density of water is 103 kgm-3 Using Bernoulli`s principle find "V"...
  28. Helios

    B Finite Universe vs. Uncertainty Principle

    If I have this right, when we have exact certainty of a particle's momentum, the bounds of this particle's location cannot be determined. Now there are some who believe in a universe of finite volume and so this particle has to be within this volume. So there seems to be a contradiction. Does...
  29. O

    Why does the Principle of Virtual Work work without higher math?

    The last chapter of most introductory textbooks on STATICS introduces VIRTUAL WORK. It is rarely taught (I studied the syllabi of colleagues). I understand the Principle of Virtual Work, having researched and studied the Calculus of Variations, Hamilton's Principle, the Lagrangian and related...
  30. KT KIM

    Apply Fermat's principle to a Concave mirror

    I am now taking optics class at my school. Fermat principle can be applied on mirror of course. Then what about Concave mirror? According to the calculus of variation. the optimized path(actual path of the light) should be the shortest path. but in the concave mirror case, it goes through the...
  31. wolram

    B Scientists evade the Heisenberg uncertainty principle

    https://www.sciencedaily.com/releases/2017/03/170322143233.htmDate: March 22, 2017 Source: ICFO-The Institute of Photonic Sciences Summary: Researchers report the discovery of a new technique that could drastically improve the sensitivity of instruments such as magnetic resonance imagers (MRIs)...
  32. M

    I Does the Uncertainty Principle restrict a particle's path?

    In the classical definition, velocity is the time derivative of the particles position curve (trajectory). The Uncertainty principle restricts the particles velocity from ever being zero. Doesn't this imply that a particles path is restricted to paths that do not have a zero time derivative at...
  33. Z

    I How Fermat's principle interprets diffraction and interference

    <Moved from the homework section> 1. Homework Statement I have read several chapters of De Brogile's article "the theory of quanta".The motion of a particle could be analogious to a ray in general optics.This is an analogy between Maupertui's principle and fermat's principle. How to use this...
  34. R

    I Does Quantum Mechanics Deny Objective Reality Before Measurement?

    "As all good textbooks of quantum mechanics have to emphasize and clarify in one way or another, it is critically important that one avoids the assumption that even before the measurement, any of the quantities that may be observed later already have some objective, particular values." Imagine...
  35. J

    I Heisenberg's Uncertainty Principle common misconceptions

    Hi pf, Please help me, the more I read about HUP, the more discrepancies I find between different sources. I found a good article that Zapper made on HUP (https://www.physicsforums.com/insights/misconception-of-the-heisenberg-uncertainty-principle/). My confusion is about the way it is...
  36. E

    An odd question regarding Bernoulli's Principle

    I don't know if anyone remembers me. I'm not a physicist but I tend to do pretty well at understanding some of the basic principles of classical physics, and that's recently created food for thought on my part.There's a message board I've found that is devoted primarily to debunking popular...
  37. M

    The Bernoulli principle from the perspective of statistical mechanics

    Hi community, I have a question about the Bernoulli principle. From statistical mechanics the pressure in the ideal gas is independent of velocity. But in the case of the flow of an ideal gas in a channel, the pressure depends on the velocity. Where can I clarify this misunderstanding...
  38. Ron19932017

    I End point information in lagrangain variation principle

    In lagrangian variation we are trying to minimize the action S = ∫t2t1 L dt. Consider a simple case of free particle. Imagine In a world that everyone one only knows how to solve ODE, Using euler lagrange equation, one has d2x/dt2 = 0 , give that we know the initial position of particle in the...
  39. MathematicalPhysicist

    B Bypassing Pauli Exclusion principle.

    Suppose that somehow we could artificially bypass Pauli exclusion principle, and make electrons or any fermions for that matter occupy more than one state at the same time? What consequences in nature will we see? what phenomenons will occur? Suppose this mechanism for bypassing is limited in...
  40. G

    Weight and the Archimedes Principle

    I was wondering - if you had a container of water and you push a hollow object that is buoyant to the bottom so that it is completely immersed - the whole container will be heavier because of water being displaced up in the container. Now if you release your hand or whatever you use to hold the...
  41. DoobleD

    B Are photons the wave sources of Huygens-Fresnel principle?

    1 - Huygens-Fresnel principle states that every point in a light wave is itself a wave source, 2 - light is made of photons, 3 - photons have a wavelength, they are QM objects. Hence my question : are photons the actual wave sources in Huygens-Fresnel principle ? Or are those two...
  42. FallenApple

    I How does the Holographic Principle relate to 11 dimensions?

    So the Holographic Principle says that our 3 dimensonal world is encoded in the 2d surface of the cosmological horizon. What about the remaining dimensions? Are they there in the regular 3space or are they also encoded?
  43. L

    Liquids: Pascal's Principle and fluid collisions

    Take a U-shaped piece of pipe, standing upwards. Fill the bottom part with liquid and leave the 'prongs' open. Now slam a parcel of liquid into one end at high speed. The other end will experience some momentum exchange and go pushed upwards. Now take the same test case and add some piping...
  44. Z

    Maupertuis's principle applied to gravity field

    Homework Statement I learned how to deriving Maupertuis's principle from Hamilton's principle under conservative energy condition and feel this interesting. But when trying to derive a particle's behavior in gravitivity field,stuck... The direction of grativity is along ##x## axis,the particle...
  45. A

    I Holographic principle, non-locality, and Lorentz invariance

    Hi all, Some recent comments from the forums here led me to do a bit of reading on the holographic principle, and to a posting on "The Reference Frame" by Lubos Moti about the (likely lack of) 'holographic noise' in the experiment by Craig Hogan at Fermilab...
  46. FallenApple

    I Einstein's Equivalence Principle.

    So if someone is in an elevator moving up at g in outer space, vs someone in an elevator in a uniform gravitational field of g, there is no way telling whether one is in an elevator in outer space or resting on earth. But what is the big insight about this? Isn't this true classically as well...
  47. N

    A Variation in Schwinger's quantum action principle

    At the moment I'm working with the https://en.wikipedia.org/wiki/Schwinger's_quantum_action_principle']quantum[/PLAIN] action principle of J. Schwinger. For this I read several paper and books (like: Quantum kinematics and dynamics by J. Schwinger, Schwinger's Quantum action principle by K.A...
  48. B

    Scientific principle about major events

    Hey everyone, I'm writing a paper about major events/turning points and wanted to cite a scientific principle. Does anyone know if there is a physics (or any scientific) principal that refers to major turning points or the specific steps that lead to a certain outcome? Thanks so much!
  49. V

    How Does Adding KSCN Affect Fe3+, SCN-, and FeSCN2+ Concentrations?

    Homework Statement During class we did a lab testing Le Chatelier's Principle where we took FeSCN-(aq) and added water in order to dilute it to a lighter colour (red to orange) and to make a stock solution. We then divided the stock solution into several test tubes. In one of them we added...
  50. muimerp

    On the proof of the Principle of Virtual Work

    I'm having some trouble understanding the proof of the Principle of Virtual Work for deformable bodies. I'll give below the proof that I've read, and, next, I'll remark what I'm not understanding. The first thing to remember before going through the proof is that the virtual work done by a...
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