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.

View More On Wikipedia.org
Recent contents Top users
  1. nomadreid

    I What is the angle in the action-angle uncertainty principle?

    There are lots of basic explanations on the Internet of the two most famous uncertainty principles, that of momentum-position and Energy-time, but I do not find any basic explanation of the action-angle uncertainty principle. I do not even know what angle (or what operator) is being referred to...
  2. Joyal Babu

    I Multiple Paths in Fermat's Principle: Which One Will Light Choose?

    In fermats principle what if there is more than one path for which the variation in optical path length is stationary.Then which path would light take to reach from one point to another.
  3. paulmdrdo

    Fundamental counting principle

    Homework Statement How many 3 digit numbers can be formed from 0 to 3 without repition Homework EquationsThe Attempt at a Solution What I did first is H = number of choices for the hundreds place T = number of choices for the tens place U = number of choices for the units digit H = 3...
  4. paulmdrdo1

    MHB Counting principle problem

    How many 3 digit even numbers can be formed from 0, 1, 2, 3, 4, 5 and 6 with no repetition? My attempt: $\frac{5}{H} \times \frac{6}{T} \frac{0}{U} = $ 30 numbers ending with zero not including two digit numbers starting with zero$\frac{4}{H} \times \frac{6}{T} \frac{2}{U} = $ 24 numbers...
  5. H

    I Radioactive decay, falling pencils and the uncertainty principle

    Consider an ensemble of identically prepared pencils balanced on its tip. If a pencil is precisely vertical, ##x=0##, and precisely at rest, ##p=0##, then it will never fall. But some pencils in the ensemble would fall, because according to the uncertainty principle, the standard deviation...
  6. H

    I Is the uncertainty principle an ontological statement?

    From the following definition, it seems that the uncertainty principle is an epistemological statement. "Heisenberg's uncertainty principle, is any of a variety of mathematical inequalities[1] asserting a fundamental limit to the precision with which certain pairs of physical properties of a...
  7. facenian

    I Uncertainty Principle: Theorem or Principle?

    Hello, It's been puzzling for me to try to understand this issue. To begin with it is clear that there are basically two principles, the Position-Momentum uncertainty and the Time-Energy uncertainty. It is also clear that there are at least two different interpretations attached to both. One is...
  8. B

    I Is Hamilton's principle an empirical statement?

    The principle of the least action, that the particle will take the path of least Lagrangian, here given as T-U, is Hamilton's principle in classical mechanics. I am wondering if this is just an empirical, experimental observation that is not mathematically driven from elsewhere, just like...
  9. M

    I Holographic Principle discussion in Sean Carroll's book

    am reading Sean Carroll's pop-science book 'From Eternity to Here' and am having trouble connecting the links in his discussion of the Holographic Principle. At the outset, I would ask that you try to answer in terms of Carroll's discussion and without moving into concepts much more advanced...
  10. E

    I Meaning of the equivalence principle in General relativity

    It is known that equivalence principle is good for understaning of general relativity (GR). This means comparison of the elevator and falling in homogenic gravitational field. But, I here somewhere something like "in the higher lever of GR, let us forget on principle of equivalence". How it is...
  11. F

    I What is the motivation for principle of stationary action

    Is the motivation for the action principle purely from empirical evidence, or theoretical arguments, or a mixture of the two? As I understand it, there was some empirical evidence from Fermat's observations in optics, i.e. that light follows the path of least time, notions of virtual work and...
  12. Absentee

    Reaction turbine working principle

    Let me start this question with a quote: "In the reaction turbine, the rotor blades themselves are arranged to form convergent nozzles. This type of turbine makes use of the reaction force produced as the steam accelerates through the nozzles formed by the rotor. Steam is directed onto the...
  13. A

    I Huygens principle introduction

    why only the common tangential surface of the secondary wavelets forms the new wavefront ? what about all the other interferances that might occur between the waves of the secondary sources , like the constructive interferances that occur slightly offside towards the inside of the tangential...
  14. TiernanW

    Help with the work-energy principle

    Homework Statement Homework Equations PE at A = 3mgx WD = Fs KE = 1/2mv^2 The Attempt at a Solution The question I am stuck on is part ii. I worked out from part i that the PE at A is 3mgx, so therefore all this must go towards the KE and the sound, and doing work against friction, etc...
  15. terryds

    How Does Le Chatelier's Principle Affect Silver Dissolution in This Reaction?

    Homework Statement For the equilibrium reaction: ##Ag^+(aq) + Fe^{2+}(aq) \rightleftharpoons Ag(s) + Fe^{3+}(aq)\ \Delta H = -20 kJ## action that can be done so more silver get dissolved is ... A. Add FeCl3 B. Decrease the pressure C. Stir the mixture D. Add FeSO4 E. Decrease the temperature...
  16. Android Neox

    I Clarifying Equivalence Principle

    Frames under identical acceleration, regardless of whether due to gravity or accelerated motion, are locally identical but time runs slower in a gravity well. For example, at the center of a large mass (like the one pictured, below) time runs more slowly than for an inertial observer far from...
  17. M

    Principle of a positive corona discharge?

    Homework Statement So as I understand, a negative Corona discharge happens between an electrode/pin/rod and a plane electrode. When the sharper electrode is connected to the negative (DC) plug, electrons concentrate on the tip, when sufficient breakthrough voltage is achieved a discharge...
  18. A

    Equilibrium and principle of moments

    Homework Statement Homework Equations Torque = F x D Manticlockwise = Mclockwise The Attempt at a Solution From what I understand, the moment on left hand side of the pivot point needs to be equal to the moment on right hand side, therefore... (Fx.2)+(5x.14) = (7xd) My initial...
  19. A

    Struggling with Electric force.... The Superposition Principle

    When I'm solving a superposition principle problem i get stuck and so confused with the signs. For example this problem Consider three point charges at the corners of a triangle, as shown at right, where q1 = 6.00 × 10−9 C, q2 = −2.00 × 10−9 C, and q3 = 5.00 × 10−9 C. Find the magnitude and...
  20. S

    The principle of least Action proof of minimum

    Homework Statement Reading Feynman The Principle of Least Action out of The Feynman Lectures on Physics, Vol 2. Link to text http://www.feynmanlectures.caltech.edu/II_19.html So I'm having a problem proving that, section 19-2 5th paragraf, that "Now the mean square of something that deviates...
  21. A

    D'Alembert's Principle: Finding Velocity of Hammer Before Impact

    Homework Statement i have a question on D'alemberts principle in which it asks me to find the velocity of a hammer immediately before impact with a pile the information i have been given is as follows: mass of hammer;300kg height of hammer;3.5m gravity to be taken as;9.81 mass of pile ;500kg...
  22. J

    I Why don't we use the Schrodinger Uncertainty Principle?

    I have read that the Schrodinger Uncertainty Principle is an extension of Heisenberg's. So, why don't we use the Schrodinger Uncertainty Principle instead of Heisenberg's? Thanks!
  23. A

    Working principle of the photodiode and photoresistor

    Hello everyone. I feel myself a little bit confused because I can't understand the difference between the working principle of the photodiode and the photoresistor. The photoresistor changes its resistance under the influence of light while photodiode changes the current across iself. Is this...
  24. J

    I Question about Uncertainty Principle

    In the Infinite Square Well problem, an energy eigenstate is in an equal superposition of two momentum eigenstates with eigenvalues that are opposite in sign(like standing waves that are formed by two wavefunctions corresponding to "opposite momentums"). So, for every energy eigenstate, we...
  25. M

    Fluid mechanics - Pascal's principle

    Homework Statement Mercury is poured into a U-tube as shown in Figure a. The left arm of the tube has cross-sectional area A1 of 9.4 cm2, and the right arm has a cross-sectional area A2 of 4.50 cm2. One hundred grams of water are then poured into the right arm as shown in Figure b. (b) Given...
  26. G

    Is there a way to calculate the entropy change for an irreversible process?

    If we consider a system to undergo an irreversible process from state 1 to state 2 and a reversible process from state 2 to state 2, then through Clausius inequality (1to2∫dQirrev/T) + (2to1∫dQrev/T) ≤ 0 (1to2∫dQirrev/T) + s1 - s2 ≤ 0 s2-s1 ≥ (1to2∫dQirrev/T) Δs ≥ (1to2∫dQirrev/T) Does this...
  27. StrawberrySaturn

    The principle of least action and diffraction

    When reading through one of the feynman lectures (http://www.feynmanlectures.caltech.edu/II_19.html) there was a paragraph that said: "In the case of light we also discussed the question: How does the particle find the right path? From the differential point of view, it is easy to understand...
  28. S

    A Theories that respect one form of the equivalence principle but violate another

    This extract is taken from Sean Carroll's textbook. It talks about a theory that respects the Weak Equivalence Principle but violates the Einstein Equivalence Principle. we could imagine a theory of gravity in which freely falling particles begin to rotate as they moved through a gravitational...
  29. W

    Deriving back focal length using Fermat's principle

    Homework Statement The plano-convex lens has a diameter of 200 mm and the central thickness of 20 mm. The edge thickness is zero and the refractive index of glass is 1.5. Find the following parameters of the lens: (i) the back focal length Homework Equations N/A The Attempt at a Solution I've...
  30. Y

    A Least Action Principle Applied to Vector Field ##A_{\mu}##

    hello, everyone. When a vector field ##A_{\mu}## has the Lagrangian of the form as ##L=Const.{\times}F^{\mu\nu}F_{\mu\nu}##, where...
  31. O

    How Can D'Alembert's Principle Help Solve This Problem?

    Homework Statement Just asking for a little help on this question 50kg object is pulled across a rough horizontal surface with a uniform force of 250N for 15m from rest, the surface has a frictional coefficient of 0.4, calculate the acceleration using dealemberts principle But this results in...
  32. alexandria

    The motor principle and direction of force on conductor

    Homework Statement Homework Equations no equations required The Attempt at a Solution can someone please verify if my answer is correct. Thanks! I used the right-hand rule for the motor principle (although another tutor on physics forum told me that its supposed to be the 'left-hand rule'...
  33. alexandria

    Electromagnetism and the motor principle

    Homework Statement Homework Equations no equations are required The Attempt at a Solution is this correct? [/B]
  34. H

    Inertial tensor remains diagonal during a shift along a principle axis

    In the middle of the below paragraph: "only if the shift vector ##R## is along one of the principal axes relative to the center of mass will the difference tensor be diagonal in that system." I suppose the difference tensor means new inertial tensor ##-## old inertial tensor. That means the new...
  35. S

    I Heisenberg Uncertainty Principle & Wave Function

    Considering how Heisenberg's uncertainty principle is applied to a top-hat wave function: This hyperphysics page shows how you can go about estimating the minimum kinetic energy of a particle in a 1,2,3-D box: http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/uncer2.html You can also...
  36. R

    On the logical-ness of the principle of superposition

    I am aware that there have been a few posts about this, I read most of them so I just want to confirm that what I've picked up is correct. The principle of superposition only applies to forces that depend linearly on some quantity (charge and mass for example), and since we wouldn't know...
  37. M

    B Einstein’s equivalence principle for a collapsed star

    The Equivalence Principle says depicting gravity as a field associated with matter is equivalent to picturing it as twisting of space. Is there a space-twisting equivalent of a collapsed star as a shell of condensed matter with interior of intense gravitational field energy (found in the field...
  38. Anithadhruvbud

    Understanding the Uncertainty Principle: Microscopic vs. Macroscopic Examples

    Can anybody give me a simple example of uncertainty principle in both microscopic and microscopic level so that I can recall it every time I read about this topic ?
  39. M

    MHB Principle Ideal in F[x] & Primitive nth root of unity

    Let ζ5 be e2πi/5. Find a monic polynomial of degree two in K(ζ + ζ−1) So, if E/F is a field extension, with α∈E then K(α) = {f(x)∈F[x] | f(α)=0} and m(x) is the minimal polynomial of α over F such that K(α) = [m(x)] where [m(x)] is the ideal generated by m(x). I was thinking maybe (x- ζ -...
  40. S

    I Intuition for Hamilton's Principle

    Is there an intuitive way to understand why nature selects the path that minimizes the action? I've seen it proven that the Euler-Lagrange equations are equivalent to Newton's laws (at least in Cartesian coordinates). So I can understand it mathematically. But on a more common-sense level...
  41. Dusty912

    Differential Equations: linearity principle

    Homework Statement Consider the linear system: dx/dt=x-y dy/dt=x+3y a. show that the function (x(t), y(t))=(te2t, -(t+1)e2t) is a solution to the differential equation (easy) b. Solve the initial value problem dx/dt=x-y dy/dt=x+3y y(0)=(0,2) need help with part b not a Homework Equations...
  42. C

    B So the holographic principle doesn't have much evidence?

    I heard the holographic principle is a sham and that there is no evidence to back it up and that 99% of physicists don't accept the idea as credible. Is this true?
  43. Roger Dodger

    Fermat's Principle, Snell's Law, and the Prism

    I have a conundrum of sorts that has made me feel like an idiot and I am hoping someone can point out my mistake. Suppose a light source is placed to the left of a prism and a detector is placed on the opposite side. I have seen plenty of pictures of this sort, and they all appear to show the...
  44. S

    Virtual work principle: equilibrium state of a system

    Homework Statement We have a system (see attached graphics) of two rods with length ##l## and mass ##m## and some external force ##F##. The coefficients ##k## of the two springs are given. The springs have no deformation when ##\varphi =0##. a) Find generalized force of the system. b) Determine...
  45. Thanshin

    I Relativity & Uncertainty: Exploring the Impossible

    There's something I don't manage to understand in the union between the relativity of simultaneity and the uncertainty of a quantum system's state. Observer A is in a lab on Earth. Observer B is approaching Earth at half the speed of light. On Earth, we build an experiment that gives a result...
  46. little neutrino

    Bohr's Correspondence Principle

    Homework Statement (a) Show that in the Bohr model, the frequency of revo-lution of an electron in its circular orbit around a stationary hydrogen nucleus is f = me4/4ε02n3h3 (b) In classical physics, the frequency of revolution of the electron is equal to the frequency of the radiation that it...
  47. H

    I Are physical constants subject to the uncertainty principle?

    Are physical constants, such as the elementary charge or the gravitational constant, subject to Heisenberg uncertainty principle, theoretically and empirically? Theoretically in the sense that infinite precision of these constants will directly violate HUP. Empirically in the sense that, for...
  48. F

    Equivalence principle and mass

    Hello Forum, What is the whole reasoning and importance of discovering that the inertial mass, which is introduced as the resistance to change the state of motion and the gravitational mass, which promotes motion (the larger it is the larger the attractive force). The equivalence principle...
  49. N

    Physics Archimedes Principle Distance an object sinks

    Homework Statement A block of wood measures 2.2m by 2.5m with depth 3.6m with weight 102KN. When placed in water, how far will it sink? g = 9.81 ms-2 density of water = 1000kg m-3 Homework EquationsThe Attempt at a Solution Volume = 2.2(2.5)(3.6) = 19.8m3 Mass = 102000 / 9.81 = 10398 kg...
  50. nikoladjal

    Demostration of the Uncertainty Principle from a given ket

    1. Homework Statement I have to demonstrate the Uncertainty Principle Starting from the expression of the following ket: |Ψa>=(ax^+ibp^)|Ψ> where a and b are complex numbers and the ^ denotes that x and p are unitary vectors. 2.Relevant equations I must use the bra-ket notation, but I...
Back
Top