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. D

    How Does Volume Change Affect Equilibrium in Gas Reactions?

    Homework Statement Hi there, I'm kinda confused about these two problems. An equilibrium mixture of NO(g), O2 (g) and NO2 (g) is allowed to expand from 1.0 to 2.0 L at a constant temperature. Given that 2 NO (g) + O2 (g) ---> 2 NO2 (g) which of the following statements is correct? (A)...
  2. M

    Problem with the principle of induction

    The principle of induction states that: Suppose\ that\ P(n)\ is\ a\ statement\ involving\ a\ general\ positive\ integer\ n.\ Then\ P(n)\ is\ true\ for\ all\ positive\ integers\ 1,2,3,...\ if\ (i)\ P(1)\ is\ true,\ and (ii)\ P(k) \rightarrow P(k+1)\ for\ all\ positive\ integers\ k. I found...
  3. B

    Particle in a box and Heisenberg Uncertainty principle paradox?

    Say you have a particle in a one-dimensional box of length L. The particle can only have momentum values of the form p_{n} = \frac{nh}{2L} according to the De Broglie standing wave condition. Now say I don't measure the position of the particle, but I know for certain that it is in the box...
  4. J

    Bernoulli's Principle (Possibly involving Venturi's Effect)

    Homework Statement Two very large open tanks A and F (the figure (Figure 1) ) contain the same liquid. A horizontal pipe BCD, having a constriction at C and open to the air at D, leads out of the bottom of tank A, and a vertical pipe E opens into the constriction at C and dips into the liquid...
  5. K

    How to solve for the angle of principle stresses

    Hello everyone, I want to start by saying this is my first official visit to the forum, however I have been using the forum for several years to help me through my classes, and I owe a big thanks to all who are involved for getting me through some tough times! Now, on to my question...
  6. L

    Entanglement and the Pauli exclusion principle

    Hey all, I have what I think (hope) is a relatively quick pair of questions regarding entanglement of fermions and bosons. First, am I right in saying that if two fermions are in the same position-state, they will necessarily be entangled? My reasoning here is just that if their...
  7. D

    Energy-time Uncertainty principle

    hi pf, i am so confused with this energy time uncertainty principle. Somewhere i find that this means law of conservation of energy can be violated for a while and somewhere i find this still being a mystery? please help me out.
  8. S

    Exceptions to the Aufbau Principle

    Are chromium and copper the only exceptions to the Aufbau Principle? If not, what are all the exceptions? Is there a list of some sort that would state all the exceptions to the Aufbau Principle? Thank you.
  9. E

    Pauli exclusion principle and fermions, bosons and quarks

    Homework Statement Which of these particles don't follow Pauli exclusion principle and thus have a symmetric wave function? a) Bosons b) Fermions c) Quarks d) All particles follow Pauli exclusion principle Homework Equations None. The Attempt at a Solution I think that...
  10. S

    Bernoulli Principle: Homework Solution

    Homework Statement Water Flows upward throw the pipe shown in the diagram at 96 L/Min. If the pressure at the lower end is 80kPa, find the velocity of the water is at both ends and the pressure at the upper end. Assume that the density of water remains constant throughout the tube and that...
  11. S

    Solving Bernoulli Principle Homework: Water Flows in Pipe

    Homework Statement Water Flows upward throw the pipe shown in the diagram at 96 L/Min. If the pressure at the lower end is 80kPa, find the velocity of the water is at both ends and the pressure at the upper end. Assume that the density of water remains constant throughout the tube and that...
  12. H

    Bernoulli's Principle with a Venturi Tube, find flow rate

    So that's the question and I'm stuck on Part b. I don't even know how to approach it. I know A1= 3A2 but I don't know A1 and I need V2 and I don't know V1 or A2. I'm just confused as to how to do this. Please help!
  13. C

    Pascals Principle: Pressure in Enclosed Fluids Explained

    Can someone explain why pressure is transmitted equally to all parts of an enclosed fluid, as stated in pascals principle ? Why doesn't the 'pressure increases with height' rule play a part ? Is it because the volume of the liquid will always stay the same? But then so what ?
  14. M

    Completeness axiom/Achimedean principle and sup set.

    Homework Statement Let B=\left\{{\frac{1}{2},\frac{2}{3},\frac{3}{4},...}\right\} Prove sup B = 1Homework Equations Archimedean principle: Let a<b and a>0 \exists n \in{N} such that an > b.The Attempt at a Solution Its trivial to see that 1 is an upper bound for B and B is nonempty, so B must...
  15. B

    What is the value of (beta) for a floating cylinder in a liquid?

    Homework Statement A circular cylinder, of cross sectional radius r = (2 + A) m, f oats in equilibrium on the horizontal flat surface of a liquid. The horizontal plane through the axis of the cylinder is parallel to the fl at liquid surface, which is very large in extent. A cartesian...
  16. B

    Energy time uncertainty principle

    Hi, Consider a laser source of frequency f. This source is projected to a target at a distance D, so that the light needs time T = D/C to reach the target. I will consider the particle behavior of light in this situation. I will study the motion of one of the photons. At the exact time T/2...
  17. C

    Doubts about heisenbergs uncertainty principle.

    Doubts about wave particle duality I know that a wave packet is formed by superposition of several individual waves having different wavelength.And the resultant wave has varying amplitudes.And from these amplitudes we can find the likeliness of the object to be in that position. My doubt is...
  18. J

    Variational Principle of 3D symmetric harmonic oscillator

    Homework Statement Use the following trial function: \Psi=e^{-(\alpha)r} to estimate the ground state energy of the central potential: V(r)=(\frac{1}{2})m(\omega^{2})r^{2} The Attempt at a Solution Normalizing the trial wave function (separating the radial and spherical part)...
  19. S

    Proving square root of 2 is irrational with well ordering principle?

    Homework Statement I know how to prove that square root of 2 is irrational using the well ordering principle but what I'm wondering is, how can we use the well ordering principle to prove this when the square root of two isn't even a subset of the natural numbers? Doesn't the well ordering...
  20. Z

    Finding Velocity at B Using Kinetics and Work-Energy Principle

    Homework Statement I have to solve this question in two ways, the first is from kinetics and kinematics and the second from the principle of work and energy. For the the first problem I obtained 3.160643122 for the acceleration at b(pulley with force t) and proceeded to find to find the...
  21. A

    Heisenberg uncertainty principle

    Hello! I have a doubt about Heisenberg uncertainty principle. Suppose that a particle moves along x-axis with a given uncertainty in velocity. Can I say something about its motion along y-axis? Thanks
  22. A

    Equivalence principle - are all accelerations actually equivalent to gravity?

    I have read the basis of the the equivalence principle, that inertial mass = gravitational mass, and that it leads to the conclusion that any acceleration = equivalent gravitational field intensity. (I believe 'gravitational field intensity' is the same as 'gravitational acceleration'.)...
  23. W

    Galilean principle of relativity and Gödel's incompleteness theorems

    Here is a question, that is so many levels above my analytical, logical, mathematical and physics skills (which sum up, in my case, to no more than popular science and science fiction reading), so the only reason that i am still asking this question, is that, not asking a question, seems to me...
  24. P

    Application of the euler equations using fermats principle

    Homework Statement The speed of light in a medium with index of refraction n is c/n, where c is the speed of light in vacuum. Notice that n ≥1: Suppose a light ray travels in the xy-plane between (x1; y1) and (x2; y2) in a non-uniform material so that n(x) is the refractive index of the...
  25. C

    Uncertainly Principle Fast Neutrons

    Hey everyone, I've been trying to figure out what went wrong here for abit now and I think maybe a fresh pair of eyes might help. If anyone could point me in the direction of my error that would be great. Thanks Homework Statement An effective treatment for some cancerous tumors is...
  26. E

    Pressure in Liquids and Pascal's Principle?

    Okay, so Pascal's Principle (as copied from Wikipedia): A change in pressure at any point in an enclosed fluid at rest is transmitted undiminished to all points in the fluid. From what I've gathered, this means that pressure in liquids act in all directions, so if you press a closed...
  27. S

    Understanding Heisenberg's Uncertainty Principle

    Homework Statement The problem and its solution are attached as TheProblemAndSolution.jpg. Homework Equations Δx = λ/sinθ Δp_x = 2h/λ sinθ The Attempt at a Solution In the equation given in the problem (Δx = λ/sinθ), why is the uncertainty of the ELECTRON written as a function of the...
  28. B

    Heisenberg s uncertainity principle

    existence of protons, neutrons nd alpha particles in the nucleus.
  29. T

    Penning ion source operating principle

    I'm sending this message to anyone who has knowledge about neutron generator. is there anyone who knows how does penning ion source works. I mean how could ions exit the holes but electrons can't exit. I didn't find any explanation about it on the web
  30. 1

    Heisenberg's Uncertainty Principle: Philosophical Implications

    I've been reading extensively around the internet and haven't been able to find a website which describes the philosophical implications of Heisenberg's uncertainty principle. Would appreciate if someone would explain these implications or provide a link in which describes them. thx
  31. Z

    Formula relating to Uncertainty Principle

    Homework Statement I was looking at a solution inmy notes which begins: ΔE = hc/λ -1st eqn ΔEΔt ~ (h-bar)/E -2nd eqn Δt ~ (h-bar)/ (hc/λ) Δt ~ λ/2∏c (where 'c' is the speed of light) What formula has been used to go from: Δt ~ (h-bar)/ (hc/λ) to Δt ~ λ/2∏c...
  32. V

    Hard Time Understanding Archimedes' Principle.

    If I have a body (for simplicity a cube with side d) on a fluid (with density ρ) with its top at a depth h, the force acting on top of it is ma = (h*d*d)*ρ*(g); where g is the acceleration of gravity, (d*d*h) is the volume of the column of liquid on top of the cube and that times ρ is the mass...
  33. I

    Question about the uncertainty principle and unit cell in phase space

    In statistical mechanics, nearly all the textbooks say that the volume of the smallest cell in the phase space of a N-particle system is h^{rN} where h is the Planck Constant, r is the degree of freedom. Also these books say that this comes from the uncertainty principle. However, the...
  34. A

    Why Must Hamilton's Principle Apply to Dependent Coordinates?

    Hamiltons principle can be used to derive Lagrange's equations IF our coordinates are independent. Thus you pretty much show that for independent coordinates Hamiltons principle is equivalent to Newtons laws. However, it seems that my book also likes to think that Hamiltons principle must still...
  35. 1

    Heisenberg's uncertainity principle

    Can someone please explain the history of Heisenberg discovered his uncertainty principle? Was he trying to physically measure the position and momentum of an electron to disprove the old atom model or did he just do it hypothetically?
  36. A

    Weak-Field Limit of Gravitational Radiation and the Equivalence Principle?

    I was just wondering if our use of a flat Minkowski background metric when looking at gravitational radiation in the weak-field limit is essentially done so that locally, for example with detectors on Earth, we can treat spacetime as being flat, but on a larger scale we use the equivalence...
  37. A

    Pascals Principle & Efficiecy related problem

    Homework Statement The input and output pistons of a hydraulic jack are respectively 1 cm and 4 cm in diameter. A lever with a mechanical advantage of 6 is used to apply force to the input piston. How much mass can the jack lift if a force of 180 N is applied to the lever and efficiency is...
  38. D

    Question about the Archimedes principle and gravity.

    Hello, I was taking a shower and started to think about balloons and helium and this question came to me: Wouldn't the things on Earth be lighter than say, a similar planet (same gravity) but with no atmosphere? (because of the push from air) I googled it but I am not sure of using the correct...
  39. K

    Many Worlds + Anthropic Principle

    This might be interpreted by some to border on the fringes on pseudo-science, but I feel logic dictates that conclusion must be one of many possibilities according to the theories. Has anyone ever considered that the many worlds interpretation combined with the anthropic principle has some...
  40. J

    Perfect cosmological principle in co-moving co-ordinates

    To quote cosmologist Ned Wright: If the Universe is the same at all times, it is argued that the value of the Hubble parameter must be a constant H_0, so H = \frac{\dot{a}}{a} = H_0 leading to an exponential cosmology a(t) = e^{H_0 (t - t_0)} where t_0 is the present age of the Universe...
  41. A

    Using uncertainty principle to find minimum Kinetic Energy expectation value

    Homework Statement Assume that a particle travels with a certain known (average) velocity ##v = \left\langle\hat{p}/m\right\rangle##. You know it's position with an uncertainty ##Δx##. Use the uncertainty principle to determine the least possible value for the article's kinetic energy...
  42. E

    Lagrangian visualisation and Uncertainty Principle

    Probably, the essence of quantum theory (QT) is principle of uncertainty (HUP). The essence of QT is also the fact that Fourier transformation of wave function in phase(?) space gives wave function in momentum space. If one wave function is Gaussian (and so both ones) this gives HUP. Very...
  43. A

    How does the reference height affect Bernoulli's principle calculations?

    Homework Statement Please click on the following link for the solution. http://s1292.photobucket.com/albums/b580/cathy12121/?action=view&current=Bernoullisequation_zps0d4485d7.jpg Homework Equations P1 + .5(rho)v12 + (rho)gy1 = P2 + .5(rho)v22 + (rho)gy2 The Attempt at a...
  44. S

    Exploring the Mach Principle: Books to Help You Understand

    some books mention one of a basis of GR is mach principle i study some text but i can't actually realize it please explain it for me or introduce some books to refer them thanks
  45. S

    Prove Heisenberg Uncertainty Principle for Ground State Harmonic Oscillator

    Ground State Wave Equation: ψ0=(a/∏)(1/4)e(-ax2/2) Prove the Heisenberg Uncertainty principle ≥h(bar)/2 by way of expectation values. First I found <x>=0 because it was an odd function then I found <Px>=0 because it was an odd function Then <x2>=∫(a/∏)(1/2)x2e(-ax2)/2dx=1/2a by way of...
  46. A

    Is Light Aware of Different Mediums in Fermat's Principle?

    I have used the attached photo to show that light takes the path described by snells law such that the time it takes from point A to B is minimized. But conceptually there is something wrong for me in this derivation. Because why would the light ray coming in, know that there is a different...
  47. A

    Gyroscope Principles: Explaining How it Works Without Math

    Can someone explain to me how a gyroscope works non-mathematically?
  48. T

    Questions on Hamilton's Principle and Quantum Mechanics

    Hi, reading Sakurai pages 102-103 (see http://www.scribd.com/doc/3035203/J-J-Sakurai-Modern-Quantum-Mechanics ) I found one thing hard to understand: If the Phase times Planck's constant equals Hamilton's Principal function in the classical limit (i.e. the action for the physically...
  49. A

    Regarding arguments in favor of Principle of Relativity

    hello.. I am reading "Relativity, the Special and The General theory of relativity by A. Einstein", and i have a few doubts that i wish to clarify. In one of the section there are two arguments given in favor of the principle of Relativity,one being that laws of classical mechanics apply...
  50. P

    Why is the work of the skier against resistance not negative?

    A girl and her sledge have a combined mass of 40kg. She starts from rest and descends a slope which is inclined at 25 degrees to the horizontal. At the bottom of the slope the ground becomes horizontal for 15m before rising at 6 degrees to the horizontal. The girl travels 25m up the slope before...
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