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. S

    I Wheeler's Mutability principle and multiple universes?

    Physicist John A Wheeler proposed the "Principle of mutability" which said that it could be the case that the universe would eventually shrink in a "Big Crunch" and the be re-born in another Big Bang. He proposed that the laws of physics (even the considered most fundamental ones) would change...
  2. Souma

    I Using general relativity to violate the uncertainty principle

    Hello everyone, Heisenberg's uncertainty principle tells us that we cannot measure the position and the momentum of a particle to infinite accuracy. My question is, can we use general relativity to overcome this difficulty? From what I know, any mass can curve spacetime even if it was small, and...
  3. S

    What is the Meaning of First Principle in Chemistry?

    Dear all, I am sorry if the topic is not appropriate in this subForum. As a chemist, I am confused by the expression of "first principle, first principles, first-principles, and first-principle calculaltion". In chemistry, we only use "ab-initio". Best regards. Youzhao Lan Department of...
  4. P

    Babinet's Principle: Effective Aperture Dipoles (Matlab)

    For clarification on "normal incidence" without drawing a picture. I'm going to assume the incoming wave has the electric field in the z-direction, the magnetic B / Auxillary H-field in the x-direction, and the Poynting Vector in the y-direction (i.e. normal to the plane of the aperture). That...
  5. J

    I Falling EM system contradicts the equivalence principle?

    The following is an improved version of my previous post https://www.physicsforums.com/threads/falling-electric-dipole-contradicts-the-equivalence-principle.964594/ Consider the following system comprising a particle on the left with charge ##+q## that is a large distance ##d## away from two...
  6. A

    Chemical reactions to depict Le Chatelier's Principle (Temperature)

    If an endothermic reaction has a lower temperature, since the forward reaction rate decreases more, the reaction should produce more energy to compensate for the decreased energy and raise the rate of the forward reaction until it reaches equilibrium with the reverse reaction. Is this saying...
  7. B

    B What happens to the uncertainty principle if....

    I just read the Feynman Lectures about the electron gun experiment with two holes in the middle wall. It demonstrates that if we don't look at the electrons while they travel toward the detector there is an interference pattern in the probability curve of the electrons similarly to what happens...
  8. A

    I The LHC: A Giant Bent Klystron Tube?

    Now the text tells that "By contrast, protons with slightly different energies arriving earlier or later will be accelerated or decelerated so that they stay close to the desired energy. In this way, the particle beam is sorted into packs of protons called "bunches". Here it refers to the main...
  9. G

    I The Cosmological Principle and the Universe

    The cosmological principle seems to hold well, and would imply an infinite amount of matter in the universe if the universe is flat and unbounded
  10. E

    A Exclusion principle in Helium 3

    I was wondering about the following question. On the one hand, Helium 3 is spin 1/2. But, on the other hand, there are multiple combinations of internal spins that would lead to total spin being spin-up or spin-down. So what would happen if we insist that all helium 3 atoms are at lowest...
  11. F

    The orgin of the superposition principle of electric field

    Isn't the superposition principle of electric field just force being addable? Jackson's electrodynamics says it's based on the premise of linear Maxwell's equations. Which support(s) the superposition principle?
  12. B

    Engineering Using the Archimedes Principle to do calculations for this floating buoy

    A Spherical buoy has a diameter of 2m and weighs 3kN. It is designed to be used in a variety or circumstances by it being floated in water and anchored to the floor with a chain. Draw the free body diagram and determine the following given that the volume of a sphere is, Volume = πD3/6 The...
  13. hyksos

    A What Fundamental Invariance Principle is Violated by FSC Anisotropy?

    If the Fine-structure constant was measured to deviate in the sky , and this deviation was directional, which fundamental invariance principle would be violated? Quasar survey by VLT has observed deviations in the FSC that appear to be locked against directions of distant galaxies...
  14. alex23

    Study the action in a one-dimensional movement (Hamilton Principle)

    Using the Lagrangian of the system I reached that ##x(t)=\frac{1}{2} gt^2+ut ## is the real trajectory of the particle. After that, I consider different trajectories: ##x(\alpha,t) = x(t) + \alpha(t)## with ##\alpha(t)## being an arbitrary function of t expect for the conditions...
  15. LuccaP4

    D'Alembert's principle on a pulley system

    This is the problem's picture: My problem is that what I got for one acceleration (m3's) via Newton's equations is not the same as via D'Alembert's principle (I've checked on my PC if they are the same expression). I can't find the mistake. Any suggestion is welcome. I attach pictures of what...
  16. B

    Principle quantum number n of the excited state

    Here is a question I have been given I have started by setting up the formula and rearranging for n_2 Only problem is that I do not know the quantum number for ground state? What value do I sub in for n_1? Any help would be appreciated! Thanks
  17. ArtVandolay

    A Extending Hamilton's principle to systems with constraints

    I'm working my way through Goldstein's Classical Mechanics and have followed the arguments until section 2.4 (Extending Hamilton's Principle to Systems with Constraints). In the second paragraph, Goldstein states that "When we derive Lagrange's equations from either Hamilton's or D'Alembert's...
  18. Yassin98

    The Equivalence Principle -- Is this a way to distinguish between a gravitational field and an accelerated rocket?

    If we are in a cabine in a gravitational field and inside, we have a racket and a ball. We put strings in each side of the racket and we connect the racket to the ceiling of the cabine. This strings only allows us to keep the weight of the racket. Then, we drop a ball to the racket. We do this...
  19. filip97

    A Huygens Principle - how to explain this with classical language?

    I was read this article(https://engineering.purdue.edu/wcchew/ece604f19/Lecture%20Notes/Lect31.pdf). I was read this paper about Huygens' principle(https://engineering.purdue.edu/wcchew/ece604f19/Lecture%20Notes/Lect31.pdf) Main idea of Huygens' principle is how wave function ##ψ(r)##...
  20. JD_PM

    Euler-Lagrange equations and the principle of least action

    Summary:: I am missing something in my integration by parts Consider the infinitesimal variation of the fields ##\phi_a (x)## $$\phi_a \rightarrow \phi_a + \delta \phi_a$$ The infinitesimal variation vanishes at the boundary of the region considered (ie. ##\delta \phi (x) = 0## at the...
  21. A

    Work-energy principle for a block fired up a vertical track

    I know how to solve the problem but have a question related to it. When the block is initially released from the spring the spring, having been pulled back, should give an initial velocity to the block. In that case why is the block's initial velocity zero?
  22. K

    I What is the name for the Heisenberg uncertainty principle?

    In quantum mechanics the name is Uncertainty principle. But outside of QM, what is the name for those inequalities?
  23. W

    I Equivalence Principle: Locally Flat Spacetimes Explained

    Hi all, I have ran into some confusion about the equivalence principle; perhaps I should state what I understand and then proceed to ask questions. It is my understanding that the equivalence principle states that spacetimes are locally Minkowski, and so the rules of SR apply in that locality...
  24. M

    Need some help with Bernoulli's principle and how it applies to a drone

    Hi there, I am building a drone for a school project and I am looking at physics behind how it flies. I stumbled upon Bernoulli's principle and the Coanda effect but I am struggling to find out how it can apply to the rotors of a drone. I understand the primary aspect of as the fluid's speed...
  25. V

    A question involving the Uncertainty Principle

    I have no idea how to approach. Hence would appreciate any help
  26. J

    Is my understanding of the working principle of a solar cell correct?

    1. Photons having enough energy to transmit an electron from the conduction band to the valence band must fall on the solar cell. 2. The cell is composed of a flat PN diode with the n-type layer on top. 3. As photons hit the n-layer, electrons and holes get formed. 4. Due to the voltage barrier...
  27. T

    Vortex Nucleation Critical velocity using the Uncertainty Principle

    Hi there, I'm very stuck on this problem when approaching it like this. I know I could use the Landau Criterion for rotons but that's not accepted here, it wants the approach to come from the uncertainty principle. My thinking is along these lines: There will be a change in chemical potential...
  28. R

    A question related to de Broglie wavelength and the Uncertainty Principle

    "Now, if an electron has a definite momentum p, (i.e.del p = 0), by the de Broglie relation, it has a definite wavelength.A wave of definite (single) wavelength extends all over space. By Born’s probability interpretation this means that the electron is not localised in any finite region of...
  29. F

    Inclusion principle sets

    Is this related to pigeon principle? $$S_1=\{1,2,3,4\},$$ $$S_2=\{2,3,4,5\},$$ $$S_3=\{4,5,6,7\},$$ $$S_4=\{5,6,7,8\},$$ $$S_5=\{7,8,9,10\},$$ $$S_6=\{8,9,10,11\},$$ $$S_7=\{5,6,2,4\},$$ $$S_8=\{1,5,7,9\},$$ $$S_9=\{4,8,10,11\},$$ $$S_{10}=\{5,7,10,11\}$$ When we choose two of them, there is...
  30. polytheneman

    D'Alembert's principle and the work done by constraint forces

    From what I understand, constraint forces do no work because they are perpendicular to the allowed virtual displacements of the system. However, if you consider an unbalanced Atwood machine, in which both masses are accelerating in opposite directions, you'll find that the tension force of the...
  31. Solitos

    Is a Biological Principle a Scientific Law?

    Hi. My understanding was that a scientific theory and law complement each other. There is a guy at work that insists that a theory with more evidence becomes a law. Recently he cited an article that said that a theory that has been repeatedly verified and appears to have a wide applicability in...
  32. stephen8686

    Heisenberg's Uncertainty Principle Question

    So with the \gamma=\frac{1}{\sqrt{1-\beta^2}} it seems obvious that relativistic momentum, p=\gamma m_o v is supposed to be used. Then \frac{ dp}{dv}=m_o(1-\beta^2)^{-1/2}+m_o v...
  33. K

    I How it's known that the variational principle works for relativity

    This question is actually about relativity and quantum field theories. I have the impression that we just use the variational principle, and given the right lagrangian, they lead to equations that we know, are correct. That seems to me a good reason for "believing" that the variationa principle...
  34. E

    Huygen's Principle doesn't necessarily imply the law of reflection

    There are many diagrams like the following which demonstrate that if A acts as a point source of wavelets, then we will have constructive interference in the case that ##i=r## as shown, as we can show with a little geometry that the path difference is zero. However, surely this isn't the...
  35. F

    Irreversible cycles, Carnot's Principle and volume-pressure diagrams

    Hi all, this question is related to a similar one I posted a couple of weeks back. Please keep in mind that the level here is high school. I'm looking for a way of describing the concepts in the title that is not overly technical. I keep circling back to these concepts because it seems to me...
  36. dRic2

    I Exclusion principle and the distance between two particles

    Hi, I'm reading the book "Quantum theory of many-particle system" by Fetter and Walecka. I can not understand the following quote from the book: Ok so the first thing I don't quite get is the part about the correlation function. I've tried to Google it a bit but didn't find anything which I...
  37. T

    Buoyancy and the Archimedes Principle

    Hello all I was hoping someone could help me with some intuition regarding Buoyancy and Archimedes Principle. I thought i understood Buoyancy in terms of pressure but when i came across Archimedes Principle I realized I did not fully understand what Buoyancy is. I have an object that is a...
  38. M

    I Integral in a variational principle problem

    Hi, I am trying to solve the problem in Griffith's book about variational principle. However, I am having trouble to solve the integral by myself that I have indicated in redbox in Griffith's book. You can see my effort in hand-written pages. I brought it to the final step I believe, but can't...
  39. Julio1

    MHB Applying Induction to Inclusion-Exclusion Principle for Probability Measures

    Show that $P(\displaystyle\bigcap_{i=1}^n A_i)=\displaystyle\sum_{i=1}^n P(A_i)-\displaystyle\sum_{i<j} P(A_i\cup A_j)+\displaystyle\sum_{i<j<k} P(A_i\cup A_j\cup A_k)-\cdots - (-1)^n P(A_1\cup A_2\cup ... \cup A_n).$ Hello, the Hint is use induction on $n$.
  40. N

    Laplace's equation vs Principle of Least Action?

    There seems to be a similarity between the solutions of laplace's equation and the principle of least action. e.g. the solution of a one dimensional laplace equation is a straight and the curve that minimizes the action is also a straight line. Was one derived from the other? Newbie here. Id...
  41. RUTA

    Insights Answering Mermin’s Challenge with the Relativity Principle

    Continue reading...
  42. S

    I Gravitational wave interactions and the equivalence principle

    According to wikipedia, the strong equivalence principle states “the gravitational motion of a small test body depends only on its initial position in space time and velocity, and not on its constitution, and the outcome of any local experiment (gravitational or not) in a freely falling...
  43. dRic2

    Jacobi's principle of least action

    I'm studying a chapter on the parametric form of the canonical equation so basically the author says that time is no more an independent variable but it is expressed as a function of an other variable called ##\tau##. In this way the canonical integral is reduced to the one I've written in...
  44. N

    How do I calculate Heisenburg's Uncertainty Principle?

    I know Heisenburg's Uncertainty Principle states that there has to be a minimum amount of uncertainty. Where the minimum uncertainty is hbar/2. My attempt at the solution Uncertainty in x = 28E-12 m (Turn pm into m) h=6.63E-34 (constant) hbar=1.055`19E-34 (constant) hbar/2 = 5.275986363E-35...
  45. J

    Royer Oscillator Working Principle

    Hi, I am studying Wireless Energy Transfer and I find Royer Oscillator in that. Ref: Wikipedia https://en.wikipedia.org/wiki/Royer_oscillator I am unable to understand how it works. I found a diagram here: Ref: https://www.smps.us/inverters.html It says that (quoted from webstie): In practice...
  46. G

    Prove expression for N using inclusion-exclusion principle

    Well ##\cup_{i} E_i## is just the event that at least one color is not used, so its probability is given by ##1- (1/N)^N##. Now if I is a subset of {1,...,N} where ##\left | I \right | = l## then ##Pr(\cap_{i\in I} E_i) = (1-l/N)^N## (I'm guessing this is where I'm making a mistake?). So then we...
  47. MPavsic

    B Lagrange–d'Alembert principle

    Hi, I am brainstorming about Dark Energy. Lagrange–d'Alembert principle is stating that sum of external forces on the system of rigid bodies and sum of system forces must be in quasi static equilibrium. What if there are no external forces acting on system of bodies and vector summation...
  48. F

    I The Equivalence Principle as a Starting point of GR

    Hello World, I have understood the following: in SR, time intervals and space intervals (distances, lengths) are relative and inertial reference frame dependent. Space and time is not absolute anymore. However, acceleration is still absolute: different inertial frames see the same acceleration...
  49. P

    A Theoretical status of the Landauer Principle

    I am interested to understand the current theoretical status of Landauer's Principle and related ideas. I am looking for key papers and results in the subject. I will highlight one key paper. An improved Landauer principle with finite-size corrections Abstract: Landauerʼs principle relates...
  50. B

    Need help with horizontal syringe Bernoulli's Principle problem.

    Did I do this problem correctly? I felt like I did this wrong because the answer is suppose to be around 50 m/s.
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