What is Couple: Definition and 445 Discussions

In mechanics, a couple is a system of forces with a resultant (a.k.a.net or sum) moment but no resultant force.A better term is force couple or pure moment. Its effect is to create rotation without translation, or more generally without any acceleration of the centre of mass. In rigid body mechanics, force couples are free vectors, meaning their effects on a body are independent of the point of application.
The resultant moment of a couple is called a torque. This is not to be confused with the term torque as it is used in physics, where it is merely a synonym of moment. Instead, torque is a special case of moment. Torque has special properties that moment does not have, in particular the property of being independent of reference point, as described below.

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  1. T

    A couple of entanglment questions

    Hi, I have some brief questions I was hoping to get some help with: 1. Can any aspect of entanglement survive measurement? What I mean is, does the so-called collapse of the wave function in some sense delete any previous entanglements? 2. Does every event (particle interactions) result in...
  2. W

    A couple few things I've always wondered:

    Just a couple tricks which are obviously incorrect, but why? 6/2 = 3 (-2)^3 = -8 (A^B)^C = A^(BC) (-2)^3 = ((-2)^6)^(1/2) = (64)^(1/2) = 8 1/-1 = -1/1 sqrt(1/-1) = sqrt(-1/1) 1/i = i/1 And then multiply both sides by i 1 = -1 So what is happening here.
  3. Y

    What are the normal forces at points A and B in a moment and couple problem?

    ive been trying to figure our this mechanics question and I am rather stuck but unfortunately i haven't had much experience with moments find the normal forces applied to the installed stud at points A and B l-----360mm--l--85-l A.==== P.=========== /==/...
  4. E

    Couple Questions Regarding REU's and Time Commitments

    I attended a seminar type thing at school regarding the path to graduate school and it was a wake up call of sorts. My eventual plan is to attend graduate school so of course anything I can do to help my application is good. I had or will have most of the requirements complete by the time I...
  5. A

    A couple of Homework questions

    Calculate the force of attraction between a K+ and O2- ion whose centers are separated by a distance of 1.5nm I think you use this equation Ea= -(A/r) but I am not sure what A is
  6. K

    A couple questions regarding pressure drop

    First, I am very confused as to the difference, if any, between head loss and pressure drop/loss. Can someone help me? Also, I know that the Darcy-Weisbach equation for head loss due to friction is hf=fL/D*V2/2g and you can plug that into get an equation for delta p that is dp=fL/D*pV2/2...
  7. E

    Couple of Electrostatics Concepts

    Momentum, Speed, Acceleration 1. Which of these is constant when a charged particle is placed in a uniform electric field? http://img638.imageshack.us/i/lol025.jpg/ 2. If an electron was placed at P, would it accelerate toward D or E? If you can't see, the bottom left charge is +4q and the...
  8. N

    Force Couple System: Explained

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  9. J

    A couple of questions about the weak force.

    Is the weak force responsible for all radioactive decay, or just beta? If it is also responsible for alpha and gamma, how does it work? If not, what causes the other two? (Also, related to this, I know that alpha radiation is two protons and two neutrons being expelled from the nucleus, and...
  10. JimiJams

    Couple simple electric force questions

    hey everyone, We're doing electric force and fields right now in our physics class. The trouble I'm having is with signs. I'm doing a prblem right now where I need to solve the magnitude and angle of electric force on one charge from a couple other charges and I don't know what sign to apply...
  11. M

    Solving Couple and Force Problem - How to Move F from O to C

    I do not understand the solution of this example. It says that in order to eliminate the last couple, we can apply the force F at another point C. But how do they move the force from O to C just like that?
  12. M

    A couple of not so simple problems from old contests

    I found some problems from old contests in my book and I need some help solving them since I could not find the solutions online. Some USA contest problems: 1.(1977.)Let a and b be 2 solutions of x^4+x^3-1=0 .Prove that a*b is the solution of x^6+x^4+x^3-x^2-1=0 2.(1983.).Prove that all...
  13. C

    Eigenfrequencies of couple oscillators

    Homework Statement I have solved for the eigenfrequencies of a system composed of two particles of masses m connected to each other by a spring of constant 2k and where one particle is connected to a wall by a spring of constant 4k and the other particle is connected to a second wall by a...
  14. P

    Couple REU recommendation letter questions

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  15. N

    Why the annihilation must be between a couple of particle and counterpart antipartic?

    Please teach me about this: Why the annihilation between particles must be particle and coresponding anti particle.Example:electron can annihilate positron create a virtual photon,after that,virtual photon create a couple muyon and antimuyon.But why can't be there exist the annihilation between...
  16. A

    Alexander & Kite: Force Needed to Hold Back

    Hi there i kinda got stuck on a couple of questions in my course book and don't understand how i am supposed to do i guess i'll focus on the first one now and post the second later Alexander is running around with his kite, the string is 25m long and the kite weighs 450g a) The string is...
  17. N

    How Do Reflections and Subspaces Challenge Linear Algebra Understanding?

    :smile: Hey everyone! I'd love if you could help me on these couple problems. Homework Statement I have attatched a PDF file (don't worry, it will only take you an instant to download - it's just a single page). I'm having problems with numbers 2 and 4. Number two is about reflections about...
  18. T

    Tennis Ball: Force, Weight, G-Force & Acceleration at 200 km/h

    Homework Statement When served at 200 km/h (124 mph), what is the equivalent weight exerted on the tennis ball? 15 kg 162 kg 200 kg 320 kg How much G-Force must a tennis ball sustain when served at 200 km/h (124 mph)? (for example the G-Force when flying a jet = 8G) 3G 50G...
  19. A

    Is the torque of a couple equal to the resultant torque?

    Homework Statement If the only forces acting in a system are a couple, will the torque of the couple be the resultant torque of the sytem? Homework Equations The Attempt at a Solution
  20. R

    A couple linear algebra questions (basis and linear transformation

    Hi guys, I have two practice problems with no solutions that i was not able to figure out. If anyone could help I'd appreciate it. Question 1 Homework Statement Find the basis of {(x,y,z) | x + y + 2z = 0} Homework Equations None? The Attempt at a Solution I can find the...
  21. D

    What are the common challenges in determining the direction of couple moments?

    Homework Statement This is not a specific homework question, but it is a coursework question. I am having trouble with determining the direction for the moment of a couple. I understand that with couples in general, there is a force negative and a force positive separated by some...
  22. J

    A couple of questions about magnetism

    ¿How do modern physicists think about magnetism? Recently, I realized something really cool that made me re-evaluate the way I thought about magnetism. I'm not a physicist, I'm in the early process of becoming one (old cow trying out a whole new career). I had this "fieldy" notion about what...
  23. S

    What is the use of a Force Couple System?

    DOUBT!..pleasez help! What is the use of a Force Couple System??..
  24. B

    What are the coordinate direction angles for the resultant couple moment?

    Homework Statement [PLAIN]http://img25.imageshack.us/img25/5139/physicsproblem.jpg If F1 = 110 lb and F2 = 300 lb, determine the magnitude and coordinate direction angles of the resultant couple moment. Homework Equations MR = \Sigmar x F, M = Fd The Attempt at a Solution...
  25. T

    Can neutrino mass eigenstate couple to the group of SU(2)

    can the neutrino mass eigenstate couple to the group of SU(2) doublet?if we intentionally not impose any flavor symmetry on it. \left(\begin{array}{c}\nu_{1}\\e\end{array}\right)
  26. M

    Restraining couple w/ vectors

    Given the following couple moments: C1=100i+30j+82k lb-ft C2=-16i+42j lb-ft C3=15k lb-ft what couple will restrain the twisting action of this system about an axis going from r1=6i+3j+2k ft to r2=10i-2j+3k ft while giving a moment of 100 lb-ft about the x-axis and 50 lb-ft about the...
  27. D

    A couple specific Physics problem solving questions

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  28. M

    Wanting to study maths but do not know where or what to couple it with?

    I have always taken an interest in maths. I like it mainly for its beauty and abstraction as its ability to solve any problem you could think of. I am going to be enrolling at university very soon and I am unsure whether I should study pure or applied. As well as that, I am not sure if I should...
  29. K

    Couple magnetic experimental questions

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  30. T

    Couple of questions on the behaviour of a Solar CEll

    Hey guys, Homework Statement Im doing my physics coursework atm and its on the subject of Solar cells and am changing a few variables and observing how the voltage of the solar cell changes. I am also measuring the current and using that to calculate the Power output. the caluclations are...
  31. R

    Gravity: Fictitious Force & Inertial Frame of Reference?

    I was reading stuff on fictitious forces and encountered a section that said that gravity was a fictitious force. I read a couple of websites but still didn't find a clear enough explanation on why this is true? Also, if gravity is a fictitious force, then doesn't that mean that so long as...
  32. A

    Couple of questions regarding theoretical physics

    I'm currently looking to major in theoretical physics/astrophysics for my undergraduate studies next year and I have a few questions about it that I'd like cleared up. At the moment, I'm a year 12 Australian high school student and I'm trying to decide exactly where and what I want to study at...
  33. B

    A convergence and divergence test and a couple integrals

    Here are five separate problems. Show that the series 1/3^(ln(n)) converges and that the series 1/2^(ln(n)) diverges. integral (sqrt(x)*e^-sqrt(x)) dx integral (x/(sqrt(x-1)+2)) dx integral (1/(2+sin(x)+cos(x) integral (1-cos(x))^(5/2)) dx There are no other relevant...
  34. R

    Ordered a couple of AoPS textbooks

    I ordered the Intermediate Algebra and Precalculus books for my precal class (half of which is covered in each). Does anyone have experience with these textbooks? Here are the links: http://www.artofproblemsolving.com/Store/viewitem.php?item=interm:algebra...
  35. D

    A couple of discrete structure questions

    1. Explain how to find a shortest path between any given pair of vertices, given the length of edges connecting the vertices and the shortest distance between vertices (after doing the shortest-path calculation) So I am given a two matrices, as said one with length of edges connecting and the...
  36. C

    A couple basic quantum mechanics questions

    Hi, I have a couple hopefully quick questions about quantum mechanics: For a momentum eigenstate how does the wave function e^{\frac{2 \pi}{h}ixp_{x}} not violate the uncertainty principle? (since both p and x are present in the function) Also, when you rewrite the above as...
  37. V

    Can torque only be caused by a force couple?

    Is it necessary that torque can only be caused by a force couple? If not, then can you provide examples?
  38. V

    Couple of questions about black holes and event horizons

    Sorry if someone already asked these, but I didn't see anything that was the same. A few of my friends are in a film class and we're working on a little indie movie, and the concept of it is a micro black hole is discovered at the edges of our solar system, and we want to make it somewhat...
  39. M

    Does the Z boson couple to photons?

    Hi I can't find a Feynman rule for the coupling of two Z bosons to a photon. Does the Z boson couple to a photon at all?
  40. R

    Intro, and a couple of questions

    Hi guys and gals, Stumbled across this forum via google. Quick introduction: I'm not involved in cosmology at all. But I do have a casual interest in it, simply because it inspires me. I'm in my mid 30s, mechanical design engineer, atheist bordering on anti-theist, but that could simply be...
  41. J

    How Do You Calculate the Motion of Rotating Objects in Physics?

    1)A baton twirler throws a spinning baton directly upward. As it goes up and returns to the twirler's hand, the baton turns through 4.42 revolutions. Ignoring air resistance and assuming that the average angular speed of the baton is 1.95 rev/s, determine the height to which the center of the...
  42. H

    Couple of Basic questions on Hole-making operations

    To improve my knowledge.. These are not homework questions :) 1. How does 'Trepanning' work and where is it used in the manufacturing industry? 2. What is the need for a 'Lip Relief Angle' in drills? 3. If 15-20 deg helix angle drills are called 'low helix angle' and 35-40 deg are called...
  43. J

    A couple question on illumination.

    Q1: Two lamps illuminate a screen equally. The first lamp has an intensity of 12.5cd and is 3.0m from the screen. The second lamp is 9.0m from the screen. What is its intensity? I know I need to use P=4*pi*(I), but there is no variable included for distance (d). Another formula given is...
  44. G

    Quick Couple Concept Questions on Guass's Law

    Just a couple quick questions I was wondering about. Also, this is an Introductory E&M class so we don't actually perform the surface integral so knowing \oint\vec{E}d\vec{A}=EA=\frac{q_{enclosed}}{\epsilon_{0}} When using cylindrical symmetry I'm supposed to ignore any flux on the top and...
  45. T

    A couple easy questions related to polymers

    1. HIPS is a : a)Polystyrene-Polybutadiene blend b)High Impact Polybutadiene Blend c)Polystyrene-Polybutadiene copolymer blended with polystyrene and polybutadiene d)High polystyrene matrix material I'm pretty sure it's not B, and I'm leaning towards C, but I'm not very confident...
  46. B

    How Do You Solve Challenging Physics Problems in Nuclear Engineering Interviews?

    Hi all, I have my interviews coming up in a bit to get into the Nuclear Engineering program with the Navy, and on one of the study guides, I was faced with these two simple energy problems, but could not figure them out for the life of me! (I graduated with my B.S. in Chemical Engineering, so I...
  47. M

    A Couple Linear Algebra Problems

    Homework Statement If A is a 4x2 matrix, explain why the rows of A must be linearly dependent.Homework Equations The Attempt at a Solution I said that nullility(A)=n-rank(A). This tells you that nullility(A) could be equal to 0,1, or 2. Since there are 4 vectors, at least two of them have to be...
  48. J

    A couple of questions about the spin of a nucleus?

    Hi, I have a couple of questions about the spin of an atomic nucleus. Say I had a carbon-12 nucleus, which is 6 protons and 6 neutrons. The Pauli exclusion principle tells us that these should be arranged in shells determined by their orbital angular momenta and spins. So, the shell...
  49. N

    How Can You Simplify These Challenging Integrals?

    Evaluate and simpfly each integral, specify u and du ∫ e^(x/3) ∫ 6 / sqrt(9x²-5) ∫ cosh(x) / sinh(x) ∫ 4x²cos(2x) ∫ (x³+4x) / (x²-4) ∫ (2^ln(x²)) / (x) from [1,2] and for this one i need to give a simplified symbolic(non decimal) answer on the first one, its simple and its confusing cause...
  50. U

    Resolving Force into Couple and Force: An Intuitive Look

    I have been doing mechanics in college and in the present chapter,two of the concepts that I found rather confusing are principle of transmissibility and resolution of force into couple and force. 1. In resolution of a force,acting,say at a point A on a body,suppose we have to resolve the...
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