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. D

    What is Archimedes' Principle?

    Homework Statement Can somebody please tell me exactly what archimedes prnciple is? Homework Equations The Attempt at a Solution [/B] So, I watched this video: . Apparently if we have a cube in a bucket of water then the mass of the whole cube is equal to the mass of the displaced water...
  2. S

    Working principle of quasi Halbach moving magnet linear motor

    Hi i can t understand the working principle of quasi halbach moving magnet linear motor. i read ''the quasi-Halbach magnetised armature generates a magnetic field which links with the single-phase stator coil, and a reCiprocating thrust force is produced as the result of the...
  3. K

    What are the units for ΔxΔp in the uncertainty principle?

    Hi all, I am reading an article about uncertainty principle. If we consider a Gaussian wave packet which standard deviation of momentum ##\sigma_p##. The uncertainty principle states that the multiplication of variance of x and variance of p is larger or equal to half ##\hbar## ##\Delta...
  4. S

    Disconnected graphs, decomposition principle

    Hi, I'm reading Schwartz's book "Quantum field theory and the standard model", section 7.3.2., page 95 (https://books.google.com/books?id=HbdEAgAAQBAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false) where he's talking about disconnected diagrams, the ones that have subsets...
  5. O

    MHB Generalization of Banach contraction principle

    Let $\left(X,d\right)$ be a complete metric space and suppose that $f:X\to X$ satisfies $d\left(fx,fy\right)\le\beta\left(d\left(x,y\right)\right)d\left(x,y\right)$ for all x,y $\in$ X where $\beta$ is a decreasing function on ${R}^{+}$ to $[0,1)$. Then $f$ has a unique fixed point. The...
  6. O

    MHB Contraction constant in banach contraction principle

    İn some fixed point theory books, I saw an expression...But I didnt understand what this mean...Please can you help me ? " It was important in the proof of banach contraction principle that the contraction constant "h" be strictly less than 1. Than gave us control over the rate of convergence...
  7. A

    Is the CMB Data Showing that We are the Center of the Universe?

    Two days ago, I have opened theme about fine-tuning on which I got good answers... Now, there is another topic, on which I have question... The reason why I am asking this question here, is because I want to get correct answer... Internet is full of trash and misinformation, and this is a...
  8. pellman

    How to measure momentum in principle?

    If we devise a physical system and perform an observation of some physical quantity, how can we infer that this quantity is related to the eigenvalues of the momentum operator -ih d/dx ? Another way to look at it. Suppose you were handed the theory of quantum mechanics and that you already had...
  9. AceTrainerBlue

    80/20 Principle for Computer Science

    I'm interested in self-learning computer science; however, I primarily only want to know the information that produces 80% of the results and mostly ignore the rest of the fluff. There's no real deadline for me. There's things that are important, yet there are also things that are cool to know...
  10. G

    Uncertainty principle if position is restricted

    Hi. Assume we have a large number of identical boxes of some finite length ##l## and with infinite potential walls. Let's prepare them all in the same momentum eigenstate. Since for eigenstates ##\Delta p=0##, by the uncertainty principle ##\Delta x## should go to infinity. However, since the...
  11. B

    Understanding Heisenberg's Principle: x and p instead of delta x and p

    Homework Statement I don't get how you can use x and p instead of delta x and p in Heisenberg's principle. Also why is it just h bar? Isn't it supposed to be h bar/2? Problem 2-iv Homework Equations delta x* delta p >= h bar/2 The Attempt at a Solution I tried to deal with this problem but I...
  12. K

    Simple Work Energy Principle Question

    I think I did most of this question correctly, but I think I might be overlooking a few steps because I might have thought about it too simply. A dinner plate of mass 510 g is pushed 60 cm along a dining table by a constant force of 3.0 N directed 22° below the horizontal. If the coefficient...
  13. bcrowell

    Runaway solutions and the equivalence principle

    The references below describe two interrelated relativistic issues that come up when you try to describe radiation from point charges: 1. We normally expect that an accelerating charge would radiate, but this would seem to violate the equivalence principle. 2. Classical E&M can't describe point...
  14. ZapperZ

    Insights Misconception of the Heisenberg Uncertainty Principle - Comments

    ZapperZ submitted a new PF Insights post Misconception of the Heisenberg Uncertainty Principle Continue reading the Original PF Insights Post.
  15. Z

    Solving for Block A's velocity: Va = 3.8 m/sThe correct answer is Va = 4.3 m/s

    Hi guys, really confusing myself over grasping this principle... I think my main problem is understanding datums and how choosing the direction of a positive axis effects the result. I understand that the work energy principle states: Wnet = ½m(vf2+vi2) I have previously been taught that Wnet...
  16. T

    Uncertainty Principle and dart of mass

    Homework Statement A dart of mass ##m## is dropped from a height ##l##. Formulate the uncertainty principle and estimate the minimum limitations, set by the uncertainty principle, of the accuracy that can be achieved in the lateral ##x## position after falling, given an original uncertainty...
  17. alex4lp

    Bernoulli's Principle equation help

    Hi everyone and thank you in advance. My first problem is: if v1=constan in a section S1, it should not be ∑ F = 0 ? Or maybe Σ M = 0 ? Because all forces that i recognize are gravity and pressure, but i never found the equation mg - PS = 0 or something similar. I was thinking about something...
  18. Vannay

    Is this statement about the Uncertainty Principle correct?

    I was reading the Feynman Lectures awhile back and I remember reading something he said about the Uncertainty Principle and it seemed slightly odd to me. I don't remember the exact quote and combing through some of the lectures online I can't quite find it. I've heard it more than once from...
  19. Mr Wolf

    Pauli Exclusion Principle: how does an electron know its state?

    This is one of those question you won't find the answer in any book. From Wikipedia: it is impossible for two electrons of a poly-electron atom to have the same values of the four quantum numbers (n, ℓ, mℓ and ms). But how can an electron know the state (the quantum numbers) of the other...
  20. T

    Solving a Physics Problem Using Archimedes Principle

    Homework Statement Homework EquationsThe Attempt at a Solution On integrating the force due to fluid pressure on the cap , I have arrived at the correct result ##ρgπR^2(H-\frac{2}{3}R)## . This in turn would be the force with which the cap presses the bottom. But I would like to solve this...
  21. D

    Archimedes principle with a completely submerged ball

    Greetings, I have a question about the classic Archimede's principle. A ball inflated with air will not sink into water. My understanding is that it will be pushed from all directions by the surrounding water trying to fill the space occupied by the ball. So there will be a pressure downwards...
  22. hideelo

    Does Fermat's principle ever give the longest time?

    I know that the way we calculate in Fermat's principle in optics is to take the path length (as an integral) and demand that it be stationary to first order. Now this approach is mathematically the same as calculating a geodesic, or finding stationary action, namely we use the calculus of...
  23. O

    MHB Why is the contraction constant important in the Banach contraction principle?

    It was important in the proof of BCP that the contraction constant h be strictly less than 1. That gave us control over the rate of convergence of f^n (x0) to the fixed point since h^n goes to 0 as n goes to infinity...If we consider f is contractive mapping instead of a contraction, then we...
  24. avito009

    Can the Pauli Exclusion Principle be explained through quantum states?

    I was reading about the Pauli Exclusion Principle and I had a doubt. This principle tells us that a maximum of two electrons can be present in an energy level and the spin of the electrons has to be in the opposite direction. But S orbital can hold a maximum of two electrons. This is fine but...
  25. E

    What is the relationship between uncertainties in position and momentum?

    Homework Statement Homework EquationsThe Attempt at a Solution
  26. J

    Heisenberg Uncertainty Principle clarification

    I found these two examples in a books which demonstrate Heiseberg's uncertainty relation...
  27. B

    Archimede's Principle and Work due to buoyant force

    Homework Statement A flotation device is in the shape of a right cylinder, with a height of 0.323 m and a face area of 4.81 m2 on top and bottom, and its density is 0.460 times that of fresh water. It is initially held fully submerged in fresh water, with its top face at the water surface. Then...
  28. evinda

    MHB Verifying the Minimum Principle for $u(x,y)$

    Hello! (Wave) Let $u(x,y), x^2+y^2 \leq 1$ a solution of $u_{xx}(x,y)+u_{yy}(x,y)+(1+x^2) e^{-u(x,y)}=0, x^2+y^2 \leq 1$. Show that $\min_{x^2+y^2 \leq 1} u(x,y)= \min_{x^2+y^2=1} u(x,y)$. Is the following right? $u_{xx}(x,y)+u_{yy}(x,y)=-(1+x^2) e^{-u(x,y)}$ $(1+x^2) e^{-u(x,y)}>0 \ \ \ \ \...
  29. J

    Heisenberg uncertainty principle calculations

    I am having some trouble understanding what to use for the uncertainties in the Heisenberg principle. My chemistry book has two problems on this principle. One asks to find the minimum uncertainty in the position of a marble of mass 1.0g given that its speed is known within +- 1.0 mm/s. The...
  30. shinnsohai

    Working Principle of Sewing Machine ( Paddle Part )

    Hi guys, I wanted to ask something that I am interested on Which is on the traditional sewing machine mechanical mechanism (On the foot paddle part) Image taken from Google. From the image above, a typical sewing machine For such application, what is the "Name" for it? Im more likely wanted...
  31. Nayef

    Work-Energy principle and spring force

    A block lies on a horizontal frictionless surface, and the spring constant is 50 N/m. Initially, the spring is at its relaxed length and the block is station ary at position x = 0 .Then an applied force with a constant magnitude of 3 N pulls the block in the positive direction of the x...
  32. Andre' Quanta

    Equivalence Principle: Einstein vs Strong

    1-What is the different between the Einstein equivalence principle and the Strong equivalence principle? 2-Is it possible to formulate the Einstein equivalence principle in this way? "For every point in space time, always exist a chart / reference frame in which the metric in that point is...
  33. A

    Minimum uncertainty of the momentum of a small particle

    Homework Statement Find the minimum uncertainty of the momentum of a small particle with mass m=1g, which is confined within a region of width a=1cm. Homework Equations Delta(p)*Delta(x)>=hbar/2 The Attempt at a Solution Delta(p)*Delta(x)=hbar/2 Delta(p)*10^(-2)=hbar/2 Delta(p)=10^2*hbar/2...
  34. Z

    Comparing the Uncertainty Principle: Griffiths vs. Shankar

    The general Uncertainty Principle is written in Griffiths' Intro to Quantum Mechanics 2nd Ed. Section 3.4, Page 109, Eq. (3.139) without dependence on the wave function itself. While it is written in R. Shankar's Principles of Quantum Mechanics 2nd Ed., Section 9.2, Page 239, Eq. (9.2.12) with a...
  35. Lance Fernandes

    Confused about the Pauli Exclusion Principle....

    The principle states that two electrons cannot have the same quantum numbers. And I've read that this applies to "fermions"- protons, neutrons, 1/2 spin particles. But how exactly does this apply to, say, a proton? Sorry if I sound stupid...I've got all my knowledge about this through the...
  36. M

    MHB Max Principle: Showing $|u_1-u_2|\leq \max_{\partial{\Omega}}|g_1-g_2|$

    Hey! :o Let $\Omega$ a bounded space. Let $u_1$ the solution of the problem $$-\Delta u_1(x)=f(x), x \in \Omega \\ u_1(x)=g_1(x), x \in \partial{\Omega}$$ and $u_2$ is the solution of the problem $$-\Delta u_2(x)=f(x), x \in \Omega \\ u_2(x)=g_2(x), x \in \partial{\Omega}$$ Using the maximum...
  37. U

    Huygens principle at the boundary of a volume

    Hi all, I have the next dude: To utilize the Huygens principle at the boundary of a volume, do we need to know precisely material properties inside the volume? Thanks!
  38. B

    Energy-time uncertainty principle

    I feel there are several non-eqivalent interpretations of energy-tme uncertainty principle.It is right?And if so,what are those corrects?In particular one that sees it (the uncertainty energy-time ) as a chance of violate conservation of energy for a time sufficently small.I would be grateful if...
  39. K

    Understanding Mach's Principle and the Existence of Objects in the Universe

    "Imagine a machine which is a box with a door. Place an object in the box, shut the door, and the machine shields all interactions between the object and the universe. When I open the box, what will I see? Will it be the same thing I would see if I had placed nothing in the box before closing...
  40. B

    Equivalence principle - light beam through a rocket

    An observer outside the rocket sees a light beam through a rocket that's accelerating. How will an observer inside the rocket see the light beam? (The problem is showed in the picture below) My friends and I had this problem at school today, and we couldn't decide which is right. Here are our...
  41. S

    Generalised uncertainty Principle Can't get rid of the i?

    Homework Statement The Attempt at a Solution As you can see where I have got up to... However I am stuck... In the solution there is no i. In mine there will be. I am unsure how you make the complex number drop out at this stage. I think I'm missing a mathematical trick here... The...
  42. Saracen Rue

    Need Help Understanding a Basic Probability Principle

    I don't really know how to explain it right off the bat, so I'm going to use an example first: Say 2 coins are tossed. Let H1 = a head is tossed first and T2 = a tail is tossed second. If you create an event space, you get {H1H2, H1T2, T1T2, T1H2}. Therefore, the Pr(H1) must equal 1/2 and...
  43. R

    What is the percentage uncertainty in V when L1-L2 is 30?

    Homework Statement My homework question says: the uncertainty in length 1 is +/- 0.1 and in length 2 is +/- 0.1 : calculate the percentage uncertainty in V where V L1-L2 is 30Homework Equations V= (1/(L1-L2))^0.5 where L is the length[/B]The Attempt at a Solution So what I did was add...
  44. mooncrater

    A relation to Le-chatelier's principle?

    Homework Statement We know about the equation: ##Fe+2HCl(g) \longrightarrow FeCl_2+H_2##. In my textbook it's written that liberation of ##H_2## prevents formation of ##FeCl_3##. But why?And how?Homework EquationsThe Attempt at a Solution I think it is related to the Le-Chatelier principle . As...
  45. J

    Heisenberg's Microscope Derive Exactly Uncertainty Principle

    Can the Heisenberg's Gamma Ray Microscope thought experiment derive the Uncertainty Principle precisely? Most derivations I find, the uncertainty is roughly 2h, whereas the uncertainty principle is "hbar over 2". Is there anywhere where there is more precise calculations to obtain "hbar over 2"...
  46. Avatrin

    Velocity of neutron using uncertainty principle

    Homework Statement A neutron in the nucleus of an atom can move in a range which is about five femtometers long. Use Heisenberg's uncertainty principle to calculate what velocities one can expect to measure. Homework Equations \sigma_p \sigma_x \geq \frac{\hbar}{2} p = \hbar k Probably others...
  47. Z

    How Does the Invariance Principle Apply to Limits in Engel's Problem?

    Homework Statement Hi Guys, This is the first exampe from Engel's problem solving book. After a long period of no math I am self studying. I do not know where my knowledge deficits lie, and was recommended this site for help. "E1. Starting with a point S (a, b) of the plane with 0 < b < a...
  48. RisingSun361

    Equivalence principle and time dilation

    I'm currently reading https://www.amazon.com/dp/0199236224/?tag=pfamazon01-20. The book claims that, according to the equivalence principle, acceleration and gravity have the same effects. So if gravity slows down time, shouldn't acceleration also slow down time? The book seems to state this as...
  49. K

    Is there a holographic principle in loop quantum gravity?

    for example, is loop quantum gravity/SF in 4 dimensions dual to a CFT in 3 dimensions? does a serious proposal of QG have to respect the holographic principle?
  50. R

    Combinatorics: Pigeonhole Principle

    Homework Statement If the 2-subsets of a 9-set are colored red and blue, there is either a red 3-set or a blue 4-set. Homework Equations None The Attempt at a Solution My book first proved for 10 points, the proof given is: Consider first for 10 points. Consider the nine edges joining one...
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