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. N

    How does Fermat's Principle follow from Huygen's principle?

    How does Fermat's principle of least time (that if light goes from one point to another, any small deviation in the path will result in a path that takes the same time on the first order) follow from Huygen's wave principle? Everyone always says that Fermat's principle can be derived from...
  2. M

    How/Why does the Mach principle define what is a 'direction'?

    I now have a general understanding of relativity but it threw up a few issues. I understand that there are no 'fixed' points of reference in the universe, which of course begs the question as to why inertia exists. The way I imagine it is if I am the only matter in the universe, then why should...
  3. J

    Archimedes's principle of float

    Homework Statement A swimming pool with 5 M length and 4 M width.A big layer of ice floats on the surface of the pool and above the layer of ice a rock with 40 KG mass and 5 R.D.,If the ice is melted and the rock fall, calculate the change in the height of water in the pool final answer...
  4. julcab12

    Death and Resurrection of the Zero-th Principle of Thermo

    ..Quick rundown on 0-th principle of thermodynamics in relation to GR and QM. Some insight on LQC-(slide to 19:07) using quantum state 'of' time in a semi-classical approximation. Fun way to think of things.^^
  5. Y

    Virtual particles and the Uncertainity Principle

    Recently, I was reading about Hawking Radiation in A Brief History of Time. It says that at no point can all the fields be zero and so there's nothing like empty space(quantum fluctuation etc.). Now, the reason mentioned was that virtual(force-carrier) particles cannot have both a precise rate...
  6. M

    Work-energy principle and conservative forces

    Hi, all there are equation in the pic but I can't understand them. I know work-energy principle which is W= F * X (work equals force times way) but I think they are special forms. What concepts and topics should I study to understand them?
  7. L

    Emergent Properties-When is the Superposition Principle Inadequate

    So I understand the Superposition principle doesn't apply to non-linear systems. I want students to understand (in high school physics...which I will be teaching in about a year) that the superposition principle essentially says things add. So I wanted to come up with some examples when this...
  8. H

    Pauli exclusion principle and position-state restriction

    Can one deduce from Pauli's exclusion principle (through the Slater Determinant) that two electrons with different spins in the same energy level, can't have the same position?
  9. nomadreid

    No-cloning and uncertainty principle

    In an explanation to distinguish the Heisenberg Uncertainty Principle from the Observer Effect, on p. 89 of "Quantum Computation and Quantum Information", Nielsen and Chuang start by writing: "The correct interpretation of the uncertainty principle is that if we prepare a large number of...
  10. E

    The Equipartion principle for diatomic molecules

    It is taught that the classical treatment of the diatomic atom would give a heat capacity of $7/2$ due to 7 degrees of freedom, (three translational momentum, two rotational momentum, on vibration momentum and on vibration position). This is based on the Hamiltonian looking like: $$ H =...
  11. P

    Why Does a Rolling Disk Have No Translational Kinetic Energy?

    Homework Statement http://postimg.org/image/m9wtlg5ah/ taking T1 for example why does the disk have no translational kinetic energy component? And why does the friction do no work? Homework Equations Kinetic energy of a rigid body in planar motion T = ##\frac{1}{2}m{v_G}^2...
  12. A

    Archimedes Principle Problem: Floating Object

    Homework Statement A cylindrical log of uniform density and radius R=30.0cm floats so that the vertical distance from the water line to the top of the log is d = 12.0cm. What is the density of the log? Homework Equations Fbouyant=Wwaterdisplaced ρwater * V displaced water = ρlog *...
  13. H

    Does QM violate the causality principle?

    Hello, As written, I am wondering if the causality principle gets violated in QM. Do virtual particles violate the causality principles? Do instantaneous events violate the causality principle? Thank you in advance.
  14. A

    Uncertainty Principle & Ground State of Harmonic Oscillator

    For the ground state of harmonic oscillator i have \Delta p \Delta x =\frac{\hbar}{2} why if i do \frac{1}{F} \Delta p \Delta x \cdot F =\frac{\hbar}{2} \Delta t \Delta E = \frac{\hbar}{2} \Delta E = \frac{\hbar}{2} \frac{1}{\Delta t} \Delta E = \frac{\hbar}{2} f but my answer...
  15. M

    Question concerning experiment on Heisenberg's uncertanity principle

    Homework Statement Hello guys my name is Mathias I'm 15 years and i have been tasked to show a little experiment in my school class. It's concerning Heisenbergs principle, you have probably all heard about this demonstration. It's basically firing a laser beam through a narrow passage...
  16. A

    Le Chatelier's principle with Fe3+

    "The Beer-Lambert relationship must be solved using a FeSCN2+ standard solution. This standard solution can be prepared by mixing a SCN- solution that has a very low concentration with a Fe3+ solution that has avery high concentration. In this situation, the reaction is driven to completion...
  17. AntSC

    Mechanics - Work-Energy Principle Question

    Homework Statement a) A car of mass 1050kg moves along a straight horizontal road with its engine working at a constant rate of 25kW. Its speed at a point A on the road is 12ms-1. Assuming that there is no resistance to motion, calculate the time taken for the car to travel from A until it...
  18. R

    Exploring Pauli Exclusion Principle: SP3 Orbitals & Electron Spin

    The 3s and 3p orbitals are filled by 4 electrons.A single atom has [Ne]3s2 3p2.But when multiple atoms get together they do so in order to minimize the overall energy.And to minimize the overall energy,the 3s and 3p orbitals hybridize to form 4 tetrahedral SP3 orbitals.And the Si atoms get...
  19. X

    Heisenberg's Uncertainty Principle

    Hi Guys, Newbie question from a layperson so please don't beat me up! :D I know that Heisenberg's Uncertainty Principle relates to measurement/observation of particles with regard to quantum physics. My question is whether or not it applies to measuring anything in the observable...
  20. carllacan

    Neutrons and uncertainty principle

    Homework Statement Using the Uncertainty Principle show arithmetically that neutrons can't be formed by a proton and an electron. Homework Equations The Attempt at a Solution I can see that if neutrons were made out of a proton and an electron they would just attract each until...
  21. K

    Heisenberg Uncertainty Principle problem

    Homework Statement Explain, using the Heisenberg Uncertainty Principle, how classical physics is reached a a limit of quantum physics when (h-bar) tends to 0. Homework Equations ΔxΔp(x) ≥ (h-bar)/2 The Attempt at a Solution The only reasonable answer I can formulate is the fact that when...
  22. T

    Deriving entropy change equation from Boltzmann's principle

    Homework Statement Show using Boltzmann's principle (S=k.lnW), show that with respect to changes in V and T: dS=k.N.\frac{dV}V{}+\frac{C.dT}V{T} Where W=T^{\frac{C}k{}}V^{N}The Attempt at a Solution S=k.lnT^{\frac{C}k{}}V^{N}=k.lnT^{\frac{C}k{}}+klnV^{N} S=C.lnT+N.lnV Now I know that the...
  23. F

    Uncertainty principle leads to superlumina ?

    According to the uncertainty principle Δp*Δx≥h/2pi, now suppose we measure a particle in a very tiny area(if x is tiny enough), s.t. Δp ≥ h/(2xpi) ≥ mc then v > c. But in fact, the velocity can not be faster than light. So how can we compromise these two statement?
  24. A

    Hot air balloon - Archimedes Principle

    Homework Statement A hot air balloon with V = 500 m^3 is floating in the air without moving. The air outside the balloon has a density of 1,20 kg/m^3, and the hot air inside the balloon has a density of 0,75 kg/m^3. Calculate the total mass of the hot air balloon. Homework Equations...
  25. S

    Fermat's principle to derive lens formula

    1. For the past 1 hour, I'm trying to derive lens maker's equation using fermat's principle, which of course is our homework. Any help would be great regarding the topic. 2. According to Fermat's Principle, optical path length OPL = PA + AQ, here PA and AQ are two rays. Now using this I...
  26. Z

    Principle of Superposition in Circuits

    Homework Statement Assume that V = 4.8V and I = 3.2mA. Find Ix in the figure using the principle of superposition. Homework Equations V=IR Kirchhoff's Current Law Kirchhoff's Voltage Law Total response = ∑responses from each individual source The Attempt at a Solution I believe I'm...
  27. T

    Helicity and the Uncertainity Principle

    Hi all! So rumor has it, that the spin of a particle is preferably aligned opposite to the direction of the particle's momentum, whereas an antiparticle spins along the direction of motion. For the sake of simplicity let us assume that the (anti-)particle is massless and hence it is an...
  28. L

    Conceptual Question regarding Uncertainty Principle

    This could be one of those questions where I'm hindered by my lack of knowledge on the subject, being only a freshman in college, but recently we learned the uncertainty principle which states that: ΔE*Δt ≥ h/4π Given this, I'm assuming it'd be accurate to rewrite ΔE as Δm*c2, which would...
  29. A

    Problem on Heisenberg's Uncertainty Principle

    The uncertainty in this principle is talking about uncertainty of measurement or particle itself?
  30. T

    Finding Voltage at Point 2 Using Superposition Method

    Homework Statement I have to find voltage at point 2 using superposition method. So, I drew one circuit with no voltage source and another with no current source, and then tried to analyze each one separately. (On the picture starting from left, its 10 volts, then 10ohms, then at top 5...
  31. L

    Uncertainty Principle Question

    Homework Statement Laser can now be designed to emit pulses of light smaller than 30 microns wide in their direction of motion. (a) Estimate the uncertainty in the momentum of a photon in such a pulse. (b) The momentum of a photon is p=h/λ. Estimate the uncertainty in the...
  32. S

    Uncertainty principle and momentum

    if you know the position why can't you know the momentum isnt p=mv and v=dx/dt its the only doubt i have so far please help
  33. M

    Brian Cox and the Pauli Exclusion Principle

    Hi, I know this is old news at this stage, but I was watching his public lecture on quantum mechanics, and he says the energy levels of all the electrons in the universe shift to adjust when he adds energy to electrons in a diamond. I understand that he should have used the phrase quantum...
  34. Y

    Bohr's Correspondence Principle and quantum theory

    Homework Statement Does Bohr's correspondence principle apply only to quantum theory? Can you give an example of the applications of this principle to relativity theory? Homework Equations The Attempt at a Solution According to my textbook, Bohr's Correspondence Principle simply...
  35. B

    Conceptual question: Bernoulli's Principle Syringes

    Homework Statement I'm interested in an explanation of the forces/principles involved in the following scenario: There are two syringes, level with one another, containing the same volume of water. The difference between the syringes is the gauge of the needle; one is of greater diameter...
  36. A

    Understanding the Minimum Energy Principle in Thermodynamics

    Confuses me. In which case is it the helmholtz free energy, the gibbs free energy, the energy that gets minimized and why? Also is it consistent with energy conservation and how is that possible if you use it on two systems exchanging energy. Can we know the total energy of the total system for...
  37. K

    Equivalence Principle: Photon Fall Near Earth's Surface

    Homework Statement A photon near the surface of the Earth travels a horizontal distance of 3 km. How far (in meters) does the photon 'fall' in this time? (Hint: think equivalence principle). Homework Equations N/A The Attempt at a Solution My understanding of the equivalence...
  38. A

    Stuck understanding Bernoulli's Principle, would love some help

    Hi all - I was having a debate with some students in my flipped class today and I can't wrap my head around Bernoulli's Principle as it relates to the sea. Can anyone explain how Bernoulli's principle works with a sail boat? I don't know how the force vectors resolve to push a sail boat...
  39. Suwailem

    Uncertainty Principle and the Second Law

    For those who read carefully the paper by Esther Hänggi and Stephanie Wehner: "A violation of the uncertainty principle implies a violation of the second law of thermodynamics": 1. Can you elaborate how extra work can be extracted if the UP is violated? 2. Does the paper implies that...
  40. H

    The Principle of Fizeau's Method: How a Toothed Wheel Helps Measure Light

    I don't know what is the principle of Fizeau's method. In the experiment a rotating toothed wheel is used.But why the toothed wheel is used? If the toothed wheel is not used,why the time for the light traveled cannot be measured?
  41. carllacan

    Using D' Alembert's Principle on an inverted cone.

    Homework Statement A masspoint finds itself under the influence of gravity and constrained to move on a (inverted) circular cone. Using D'Alembert's Principle find the equations of motion on cylindric coordinates. Homework Equations D'Alembert's Principle: (\vec{F_a}...
  42. B

    Derive a formula from the uncertainty principle

    Homework Statement Derive from the uncertainty principle a formula for the relative spread of the spectral line that corresponds to the longest wavelength of the Lyman series. Homework Equations uncertainty principle: σxσp≥\hbar/2 planck constant \hbar=h/2pi h=λp Lyman series...
  43. M

    D'Alembert's Principle:- A Falling Box

    I've been asked to research D'Alembert's principle and solve a question. I've looked up quite a lot of different explanations on the internet of D'Alembert's Principle and I'm not quite grasping how to use it. I understand that you rearrange formula so that they equal 0 (e.g. f - ma = 0 or PE -...
  44. Q

    Anthropic Principle and Infinitely Minute Variations

    Let's assume as per the anthropic principle, for the mere sake of argument alone, that the physical constants of the universe are indeed biased towards life and that any significant change would eradicate the possibility of any form of conscious life. For the sake of argument as well, let's...
  45. I

    Equivalence Principle: Paper on Internal Observer Effects

    Hi! How this paper relates to the equivalence principle? http://arxiv.org/pdf/gr-qc/0701084.pdf "in contrast to the situation with static gravitational forces, the effects of accelerative gee-forces on the internal observer are increased"
  46. H

    Can heisenberg uncertainty principle be beaten by fast measurements?

    I don't know much about physics but just had this idea: As I understand it the HUP prevents good accuracy of a small object's momentum and position at the same time. Assume trying to measure the momentum and position of a single atom. In theory, can't we get a very good idea of both of...
  47. K

    Principle of Moments: Restoring Forces Explained

    This has botherd me for quite sometime ...imagine a beam or a simple scale supported at its centre and carrying equal weights on two extreme positions on the scale from the centre, now under equilibrium the scale will be horizontal...now my question is if one of the weight is lowered by action...
  48. Quarlep

    Understanding the Equivalence Principle and Einstein's Curved Spacetime

    Hi I am reading Stephan Hawking's Universe in the Nutshell and there I didnt understand this sentence "This equivalence didn't work for a spherical Earth because people on opposite sides of the world would be getting farther away from each other.Einstein overcome this idea to make spacetime...
  49. Spinnor

    Fair and unfair N-sided dice in principle.

    In principle does classical physics allow us to make a fair N-sided die where N ≥ 3? If I give you a set of N positive numbers n_i whose sum is 1 can a N-sided die be made in principle such that each face of the N-sided die comes up on average with a probability n_i? Can N above be reduced to...
  50. S

    Bernoulli principle and venturi effect.

    I have a specific problem involving two reservoirs filled with water with a height difference Y and total head H, and was wondering if a venturi like device could be used to calculate the resulting pressure head x and if it will exceed the bottom of reservoir 1. Also the drain length is d...
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