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. M

    Motor Principle and Magnet on Balance

    Hi everybody. This is my first thread ever on this forum :S I'm in a first year physics class, and the other day we did a lab involving a c.c.c (current carrying conductor) and a magnet on a balance. The c.c.c was a wire which completed a circuit. One had a magnet assembly which was placed on...
  2. Ahmed Abdullah

    Equivalence of waveparticle duality to uncertainty principle

    http://www.sciencedaily.com/releases/2014/12/141219085153.htm It says "Here's a nice surprise: quantum physics is less complicated than we thought. An international team of researchers has demonstrated that two peculiar features of the quantum world previously considered distinct are different...
  3. BrainMan

    Calculating Buoyancy: Solving for the Height of a Boat in Salt Water

    Homework Statement A small boat weighing 1000 N has a surface area of 3 m^2. It floats only 5 cm above the water level when in a fresh-water lake. How high out of the water will it ride in a salt-water lake? Assume the surface area of the boat does not change as it rises (salt water has a...
  4. EternusVia

    Principle of Least Time Question

    Hi everyone, I'm taking my second semester of calc based physics this coming spring. I have a question in optics stemming from my reading of Feynman's lectures on physics. He gives a rough definition of Fermat's principle of least time as follows: "... out of all possible paths that it might...
  5. S

    Inclusion-Exclusion Principle and Circular Arrangement

    6 people are invited to a dinner party and they are sitting on a round table. Each person is sitting on a chair there are exactly 6 chairs. So each person has exactly two neighboring chairs, one on the left and the other on the right. The host decides to shuffle the sitting arrangements. A...
  6. P

    Understanding the Potential Energy Principle

    Homework Statement how to prove the potential energy principle? how do you make sense of the potential energy principle ie -dU/dX = F(x). What does the principle really mean? Homework Equations -dU/dX = F(x) where U is the potential energy and F the force. The Attempt at a Solution Not...
  7. S

    Intuition behind Hamilton's Variational Principle

    Background: I am an upper level undergraduate physics student who just completed a course in classical mechanics, concluding with Lagrangian Mechanics and Hamilton's Variational Principle. My professor gave a lecture on the material, and his explanation struck me as a truism. Essentially, he...
  8. L

    D’Alembert’s principle and conservation of energy principles

    Homework Statement A load of 10 kg is pulled up a lubricated slideway, set at an angle of 30° to the horizontal, such that the load is accelerated from rest to a velocity of 1 m/s whilst traveling up the plane through a distance of 1 m. The frictional resistance to this motion is 10 N and g =...
  9. B

    Light speed and uncertanty principle

    Is it true that if time stood still it would violate the uncertainty principle. therefor if you traveled at the speed of light time stands still and you would violate the uncertainty principle. if this is true does that sugest that QFT sets a lower max speed that matter can travel at than what...
  10. M

    Holographic principle and string theory

    Hi. I am no physicist but I am trying to know something about the holographic principle. As I understand, everything is happening in a surface and our three-dimensionality is an illusion of our senses. On the other side, string theory assume the existence of 11 dimensions. Are the two theories...
  11. Mike Dacre

    Archimedes Principle - Mass floating on ice

    Homework Statement Question: What minimum volume must a slab of ice in a freshwater lake have for a 50.0kg woman to be able to stand on it without getting her feet wet? Homework Equations Archimedes principle...
  12. Q

    Principle of impulse and momentum

    Homework Statement In the gear arrangement shown, gears A and C are attached to rod ABC, which is free to rotate about B, while the inner gear B is fixed. Knowing that the system is at rest, determine the magnitude of the couple M which must be applied to rod ABC, if 2.5 s later the angular...
  13. E

    Buoyant Force and Archimede's principle

    Homework Statement A balloon used for a physics experiment has a radius of 3.15m and is filled with helium. The total mass of the balloon is 15.2kg and the density of the surrounding air is 1.28 kg/m3. a. How much buoyant force is acting on the balloon? b. When the balloon is released from the...
  14. throneoo

    Uncertainty Principle and single-slit diffraction

    Homework Statement A beam of 50eV electrons travel in the x direction towards a slit of width 6 micro metres which is parallel to the y direction. The diffraction pattern is observed on a screen 2 metres away. Use the Heisenberg uncertainty principle to estimate the minimum uncertainty in the...
  15. T

    Resources for variational principle to solve coulomb problem in D dimension

    Hi, i have been struggling to find some good resources on variational principle , I have got an instructor in advanced quantum course who just have one rule for teaching students- "dig the Internet and I don't teach you anything".. So I digged a lot and came up with a lot reading but I need...
  16. R

    Wave Particle Duality & Uncertainty Principle: Which Came First?

    Which of them comes first,(I mean the concept or the theory)? Did Heisenberg come up with the idea of uncertainty principle because of the discover of the wave particle duality? Thanks for paying attention~
  17. A

    Direction of magnetic field and physics principle?

    Homework Statement A proton traveling at a speed of 3.00*10^6 m/s north through a magnetic field experiences a force of 1.50*10^-14N up. What is the magnitude and direction of the magnetic field? Include the physics principle Homework Equations Fm=qvB[/B]The Attempt at a Solution I solved for...
  18. S

    Entropy: Joules per Kelvin Explained

    Whilst I understand that entropy is a measure of the number of specific ways in which a system may be arranged. The units for entropy don't make sense to me intuitively. Why joules per kelvin? What way at all does that show how "disordered" a system is. When I hear joules per kelvin, I think of...
  19. putongren

    Unified Field Theory: Different Principle or Too General?

    If Classical Physics (Newton, Maxwell, Einstein) operates on the principle of determinism and causality, Quantum Mechanics operates on the principle of probability, then would the Unified Field Theory (or Theory of Everything) operate on a yet different principle? Or am I being too general?
  20. H

    Can Jensen Receive Same-Time Signals from Sensors?

    Hi! Question: Is the following possible in principle or am I missing some important rules in relativity which makes it impossible? Imagine a spaceship which can travel at relativistic velocity. It is 10 kilometers long and equipped with two sensors, 1 and 2, placed in each end of the ship...
  21. E

    Frank-Condon Principle - Potential Energy Surfaces

    Theory and my Understanding: So I understand how the frank condon principle let's us effect electronic transitions instantaneously, since the motion of nuclei (on the timescale of such electronic transitions) is quite slow. Consequently, when a photon of light is absorbed you can have an...
  22. G

    Bernoulli Principle and fluid velocity

    I have been trying to fully understand this concept of Bernoulli's Principle , the Venturi effect and fluid velocity and energy. I need to grasp this to develop an idea that I have been working on. 1. As water is forced down a narrowing pipe, as the pipe gets more narrow, it means it losses...
  23. R

    Description of the Electron Degeneracy Principle

    I understand that the electron degeneracy principle states that no two electrons can occupy the same space at once. However, I do not think I clearly understand the physics behind that. I talked to my physics teacher about this and he said it had to do with the electron spin; I thought it was...
  24. adoion

    Exploring the Principle of Least Action in Physics

    hi, please if somebody could explain why anybody would consider the "action" and is there any proof that the minimal action actually gives the correct route of a problem?
  25. UncertaintyAjay

    The Uncertainty Principle Uncertainty

    My friend and I had this argument about whether or not the uncertainty principle is applicable to stationary particles. I maintain that it is, because the principle is really about predictability ( isn't it?) But he maintains that it doesn't. So I would just like to clear things up . Does it or...
  26. P

    The (non-?) flatness of a uniform gravitational field and the equivalence principle

    Desloge (1989) published the article: ## '##Non-equivalence of a uniformly accelerating reference frame and a frame at rest in a uniform gravitational field## '##. His result, briefly resumed: a uniform gravitational field is not flat, is quite interesting. But the way he proves the result is...
  27. Alexandre

    What's the difference between principle, law, rule, theorem and equation?

    Well, I do understand what mathematical theorem means, and I also know what differential equation is but I don't really get why sometimes certain things are called "equations" instead of "law" (Maxwell's equations, nobody calls it Maxwell's laws) and conversely some equations are called laws...
  28. O

    MHB Fermats Principle: Find Time of Travel Along Path APB

    How do I find the time of travel along a path say APB of tetha and show it's maximum at P= P(0) considering a ray of light traveling in a vacuum from A to B with reflection at P in the same vertical and as A and B, according to the law of reflection,the actual path goes via point P(0) at the...
  29. ORF

    Is the principle of minimum action applicable to nonholonomic systems?

    Hello Is the principle of minimum action applicable to nonholonomic systems? Why? If this question is already answered in this forum, just tell me, and I will delete this thread. Thank you for your time :) Greetings PS: My mother language is not English, so I'll be glad if you correct any...
  30. R

    Basic Heisenberg uncertainty principle stuff

    Homework Statement A bullet is shot from a rifle. 1) if the position of the centre of mass of the bullet perpendicular to its motion is known to have an accuracy of 0.01 cm, what is the corresponding uncertainty in its momentum? 2) If the accuracy of the bullet were determined only by the...
  31. E

    Principle of work and energy to a collar and spring system, been stuck for hours

    Homework Statement I've been attempting this problem all day now. My current submissions are 10.6N and I keep getting 7.04N every time I retry it but this is also wrong. Can somebody please help me out so I can figure out what I'm doing wrong? Thanks for any help in advanced! The 3.35kg collar...
  32. T

    Can You Verify My Calculations on Spring Compression and Energy Transfer?

    First off I just want someone to check and see if I got the right answer because I have no way of telling if it is the right answer or not. I am pretty sure I have the right answer but I have no way of checking. 1. Homework Statement A spring with a stiffness ks and relaxed length L0 stands...
  33. B

    Calculating Principle Moments of Inertia

    Hi Folks, Is it possible to calculate the principle moments of inertia acting along the principle axes of inertia given the moments of inertia and their directional vectors. Ie , I have the following information Moments of inertia ##J_1, J_2,J_3=18kgm2,15kgm2,6kgm2## and the directional...
  34. T

    Uncertainty Principle mechanics

    Can one use uncertainty principle for Classical mechanic wave and still get the same equation for Quantum mechanics, as in (root-mean square uncertainty of position) (" of momentum) > hbar/2? It's just that V(x) [Potential equation] is same for both Classical and Quantum mechanics so I wonder if...
  35. Nim

    How does the Holographic Principle apply to different scenarios and dimensions?

    I first came across this concept in a Scientific American magazine. At the time it was nigh impossible to find much more information on it. Even now I am having a hard time wrapping my head around it. So I have a few questions. From what I understand, it basically says: Every single bit of...
  36. R

    Understanding the Principle of Birefringence: Δn Explained

    I finally understand the principle of being able to imagine light as having 2 perpendicular components of electric field, to use an analogy from an earlier thread, its just as a weight on a slope may be considered to have 2 componants. Anyway, for this example nx = ny = no and nz = ne. Light is...
  37. N

    Principle of Virtual Work and static equilibrium

    Homework Statement The system shown in Fig. 2-6 is in static equilibrium. Use the principle of virtual work to find the weights A and B. Neglect the weight of the strings and the friction in the pulleys. Homework Equations Conservation of gravitational potential energy. The Attempt at a...
  38. J

    How Does a Resistor Affect Current Flow While Maintaining Consistency?

    Dear all, I would like to ask you one basic thing. I know exactly how resitor works on electrical base. But I want to know if I know good how it works on physical base. This is my knowledge from primary school (for basic circuit). Input current and output current in circuit is still equal. This...
  39. P

    That Heisenberg Uncertainity Principle

    Does the Heisenberg Uncertainity Principle mean: 1) If a particle is confined within a length x then it must jiggle around with a momentum given by p ~ h/2x PI OR 2) If we measure the position of a particle to an accuracy of x then its momentum will be uncertain by ~ h/2x PI
  40. Just_some_guy

    Using the principle of conservation of energy

    Hi all, I'm not 100% sure this belongs in this topic but it was a problem I was given in a quantum mechanics lecture so here goes, sorry if I am wrong.Anyway I was given a hamiltonian H= T+VWhere T is kinetic energy and av is potential, and asked to use dH/dt= 0 to find an analogy between...
  41. _N3WTON_

    The Principle of Superposition for Homogeneous Equations (DiffEq)

    Homework Statement Verify that e^x and e^-x and any linear combination c_1e^x + c_2e^{-x} are all solutions of the differential equation: y'' - y = 0 Show that the hyperbolic sine and cosine functions, sinhx and coshx are also solutions Homework Equations Principle of Superposition for...
  42. L

    Uncertainty principle for electron inside atom

    Homework Statement Hopefully it is not a faux pas to post two questions relatively close together in time. This is more of a conceptual question than a calculation based question. An electron is confined to a region of space of the size of an atom (0.1 nm). a) What is the uncertainty in the...
  43. M

    Transformer principle (induced secondary voltage/current)

    Homework Statement Draw a sketch and show/explain how the induced secondary voltage and current "moves" when the primary current "breaks" the instant the switch N is opened. See the attached image below (I apologize for my awful paint job...). Homework Equations The Attempt at a Solution...
  44. A

    A problem about virtual work principle

    hello, I want to apply the virtual work principle to a continuous mechanical system to derive equilibrium equation, naemly, a long thin bar with one end fixed in the wall and other end applied with pressure P. but I can not derive the correct equilibrium equations. I hope some expert could give...
  45. A

    A problem about virtual work principle for continuous system

    dear all, the virtual work pinciple can be used to derive the equilibrium equations for the mechanical systems. however, when I want to apply it to a continuous system, I found it can not give out the simple equilibrium equations. there should be something wrong with my thinking. I expect some...
  46. E

    Equivalence Principle in muon experiment?

    Someone noted that the famous muon half-life experiment, supporting time dilation in SRT, seems to violate the equivalence principle of GRT. The very large radial acceleration in the experiment does not appear to cause any additional slowing. The acceleration does not seem to have an equivalent...
  47. H

    Curie's Symmetry Principle and Heterogeneous Thermodynamic Systems

    I am trying to understand the (possible) couplings between scalar chemical reaction phenomena and vectorial phenomena such as heat conduction and mass diffusion. It is argued in the literature that I have read that the usual assumption of cross coefficients for scalar+vectorial phenomena only...
  48. e2m2a

    Mach's Principle & Local Fields: A Discussion

    One argument against Mach's principle is the speed of light restriction. How could the distant cosmic mass of the universe instantaneously have a local effect on an accelerating mass? But could we view this from the perspective of a field that is already presently locally at all points in...
  49. F

    Quantum Mechanics / Uncertainty Principle Question

    Homework Statement The square of a wave function gives the probability of finding a particle at a given point. What is the probability of finding an electron in a 1s orbital within a volume of 1pm^3, centred at: a) the nucleus b) 50pm away from the nucleus? Homework Equations...
  50. AbhiFromXtraZ

    The Principle of Invariant Light Speed

    While reading Special Theory of Relativity from Feynman Lectures, I fell into the confusion about invariant speed of light. What I'm asking for is an explanation about this. No matter whether physical explanation or mathematical. So my question is Why the speed of light is same for a person...
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