Couple Definition and 445 Threads

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. nav888

    How does the calculation of work change for a rotating or non-rigid object?

    Here is the question, I am struggling with it as in all the past questions I have done it didnt matter if you worked out the work done by each force and then added it all together or if you added the forces together and then worked out the work done by the total force, but here the net force is...
  2. Leo Liu

    What is bending moment? Is it a moment couple? Why?

    In engineering statics I've learned the concept of bending moment, which in some way indicates an applied load that tends to bend the object, and it seems that it can move around freely in the reference frame. (I understand moment in engineering is not quite the same concept as torque in physics...
  3. M

    I just have a couple questions about parts on an F-16

    Hello I am just curious about something. In the image above, the spike shaped thing at #1, and the long thing at #2, what are those and what are their purposes? Since I don't know what they're called I can't google them lol. My current guess is that #2 is a mount for missiles, and #1 has...
  4. BiGyElLoWhAt

    I A couple questions about the Riemann Tensor, definition and convention

    According to Wikipedia, the definition of the Riemann Tensor can be taken as ##R^{\rho}_{\sigma \mu \nu} = dx^{\rho}[\nabla_{\mu},\nabla_{\nu}]\partial_{\sigma}##. Note that I dropped the Lie Bracket term and used the commutator since I'm looking at calculating this w.r.t. the basis. I...
  5. T

    I Understanding the Behavior of a Couple: Exploring the Concept of a Free Vector

    Hello (Everyone here has been so helpful -- thank you. Things I thought I knew, I now doubt; and this is so helpful to have this group.) There is an current discussion on Yaw. I am enjoying that. And that raised an issue for me. However, I do NOT want to hijack that thread, so I am posting...
  6. G

    Forces proportional to the sides of a quadrilateral result in a couple

    Can I please ask for help with the following: Forces proportional to the sides of a quadrilateral taken in order act respectively along those sides. Prove that the resultant of the system is a couple whose magnitude is represented by twice the area of the quadrilateral. Not sure where to start...
  7. Abdullah Almosalami

    Couple Questions about this Resistor Datasheet

    So I have these 10k 5% resistors from Stackpole Electronics and just because I never actually took the time to look at a resistor datasheet beyond nominal resistance, tolerance, and power rating specs, I decided to look them up. Came across a couple things I wanted to ask about: 1) Maximum...
  8. S

    MHB Couple of hard trig questions....

    Hi, I was hoping to get some help on these five questions, I've been stuck on these and any help would be greatly appreciated! 1. Inflation rises and falls in a cyclical manner. If inflation is highest at 4.8% and lowest at 1.3%, what c for the equation y = a sin(k(x + d)) + c? 2. If the...
  9. Z

    Creating a Graph using MS Excel -- help with a couple problems please

    Hi, I want to create a graph from the following data. The data is related to 3 different computers but the fields are same: Please provide me the steps. Garph1 BS CPU Percentage 12 Memory Usage 15773696 sdiskusage total 9.82901E+11 sdiskusage used 1.41429E+11 sdisk usage free 7.91472E+11...
  10. G

    NMR: Why do "identical" nuclei not couple with each other?

    Hello there, Spin–spin coupling is encountered in the majority of NMR spectra. However, it does only occur when the two interacting nuclei are non-"identical". But why is the coupling not occurring between "identical" nuclei? I have been wondering about this because I could not think of a...
  11. F

    What Is the Instantaneous Center of Rotation and How Is It Chosen?

    Hello, A force couple is compose of two forces of equal magnitude, opposite direction and parallel lines of actions separated by a distance ##d##. The moment due to a force couple is called a pure moment because its value does not depend on the point about which the moment is computed. The...
  12. Andrea Vironda

    How does the thickness of a clamp affect its ability to transmit torque?

    Good morning sirs, let's imagine a cylinder, surrounded on 360° by a coating of the same shape. I can close the 2 half using 2 bolt screws. what's the maximun transmittable torque? here's a scheme: i would to consider the sum of forces as a normal force on the top of the cylinder, producing a...
  13. C

    What are some common misunderstandings about magnetism and relativity?

    Hello, there are a couple things about magnetism that I do not understand. 1. Why didn't we define the magnetic field to be in the directions of the force? This isn't really a technical question, I am just more curious about why it is this way. The way I was thinking of it, the math seems to...
  14. L

    I What does coupling mean in physics?

    I am reading Carroll’s Spacetime and Geometry, and I have seen the word “coupled” used multiple times in seemingly different ways. I have gotten the sense that it means some sort of interaction between particles, but Carroll refers to coupling between matter fields and the curvature of...
  15. M

    A couple of questions about antennas, bandwidths and power

    Does it take more electrical energy to transmit HF and lower frequencies than it takes to transmit VHF and above? Are there any wavelengths beyond radio waves and gamma rays? Is it true that the lower the frequency, the lower the amount of data that's being sent? I read on this wiki that...
  16. opus

    A couple basic questions about finding a limit

    Homework Statement Find the following limit: $$\lim_{x \rightarrow 10}\frac{x-10}{4-\sqrt{x+6}}$$ Homework EquationsThe Attempt at a Solution [/B] Please see attached work. I have a few questions (other than if my solution is correct or not). First, is at step (ii)(C): What makes me uneasy...
  17. F

    B A couple of links about, not from science

    We repeatedly receive some fundamental questions, some of them of philosophical nature, which we're not very keen to answer - not because they weren't legitimate questions, but because we made the experience, that they simply lead nowhere, and, I'll have to admit, because of the lack of...
  18. lc99

    How to Calculate Moment of a Couple Using Cross Products?

    Homework Statement Homework EquationsThe Attempt at a Solution I am confused. It looks like the couple forces are at a angle pointing to the x axis. So i did moment about a axis of that angle. I found this angle/axis unit vector to be (-0.6i -0.8j) Then i found the moment couple about the x...
  19. K

    B A couple of questions about photons and superposition..

    There are two polarization filters, A and B. Polarization filter A has angle of 0° and B has an angle of 30°. A photon is in superposition, so it doesn't have a definite polarization axis. The likelihood it's passing through a filter is depend on the difference between angle of the...
  20. S

    I have a couple questions about Arduinos

    Hello, I need to use the 0 and 1 digital pins while I have a motor shield on. I will include the link to the shield I plan to buy. Is it possible to solder a wire on top of the 1 and 0 pin (on the shield itself) while having no problems? I circled the pins I am talking about in an ugly green...
  21. U

    Admissions Submitted all of my applications a couple weeks ago

    Anyone else going through this process? I thought I would be relieved once I submitted everything, but now I just feel worse! I know I won't be hearing back from places until probably late February at the earliest, but having to just sit here and wait to hear back is brutal. To those of you...
  22. Francis Hannah

    Resultant force-couple system where resultant couple is 0

    For the structure, find the distance from O (in direction OA) to the point where the resultant force-couple system of the forces shown should have a resultant couple of zero. Give answer in metres. a=90 N, b=289 N, c=549 N Clockwise negative, anticlockwise positive. Moment at a =...
  23. F

    How can I draw the resultant force of the couple M, F1 and F2?

    I'm supposed to express the reultant force R of M, F1 and F2 in terms of F1, F2, r, s and α. But I need to know how to draw R first. How can one do this? Does the couple create a force uppwards from O? Can I move F_1 and F_2 also to the origin and combine the forces? Here is the image:
  24. K

    B A couple of questions about diodes and the depletion region

    In a diode, we have N side, P side, and a depletion region, made of positive and negative charged sides. N side and P side of the diodes are neutral charge. In N side there are free electrons. In the positive charged side of the depletion region, there are positively ionized atoms that "lack"...
  25. yecko

    Moment couple (opposite direction on same line)

    1. Homework Statement It is a part of the question in my homework and I extract this out just for the part i m confused(in the picture above) Homework Equations Moment couple=d*F [d is the difference in point of application (=sqrt41) or the perpendicular distance of the forces(=0) ?] The...
  26. yecko

    Is my approach correct for the 3D moment couple problem?

    Homework Statement Homework Equations M=r x F = d * F (for moment couple) The Attempt at a Solution This is my attempt to the question, yet I have got quite a different answer from my classmates... (especially the moment by the 50N force couple) Can anyone point out is there anything wrong...
  27. marsupial

    Equivalent force and couple moment

    Homework Statement I will post a photo of the question in the thread once I've created it. I have found the magnitude and angle of the resultant force, but I am unsure of how to proceed. I find moments and couples confusing. Homework Equations $$\vec M = \vec r \times \vec F$$ The Attempt at...
  28. Jamison Lahman

    Fiber Optic Coupling -- how to couple a 200μm core fiber into a 50μm core fiber?

    Is it possible to couple a 200μm core fiber into a 50μm core fiber by using a 4x magnifier/reducer?
  29. Nikhil N

    How to choose an amplifier to couple the noise into data line

    Hii... I have to couple the noise into a communication cable for analyzing the performance of the communication. I am using a function generator which will generate a white noise of 1-2V(rms) and I have a current transformer to couple this to the communication line. The current transformer has...
  30. Averagesupernova

    Couple of interesting electrical things in an old house

    While cleaning out an old house I found this book. I have later (much) copies of this book that I often refer to. A little mouse chewed but nonetheless a nifty find. Was amused there is a chapter on knob and tube wiring. - -
  31. P

    General equivalent couple - force system

    Homework Statement Hello gentlemen! I came across a real challeging problem about static, which states the following: assume a force system is equivalent to a force \vec{F}_{1} and a couple M_{1}\vec{k} acting at a point \vec{r}_{1}. Find some point \vec{r}_{2} and a force \vec{F}_{2} so that...
  32. N

    I Resultant force after adding a force to a couple moment?

    I don't get it. Imagine there is a stick leaning aganist a wall. There is a moment couple somewhere on the stick. The end of the stick hits the wall and the wall acts against it. The sum of moment is 0 but since the moment couple forces cancel each other, the resultant force is the wall...
  33. Frankenstein19

    Help with Statics -- Moment of a Couple

    Homework Statement This is the problem I'm having problems with. Homework Equations M=F x r The Attempt at a Solution Let me explain what I've been doing with the practice problems before it, because I fear I may have the wrong understanding. For this exercise I just found the...
  34. A

    Programs A couple of questions about applied physics Ph.Ds

    I hope this isn't too much for one thread, but I have a couple of questions regarding applied physics Ph.D programs. 1. Are there a lot of schools that offer degrees in applied physics, and what are some of them? I've found programs at places like Cornell, Stanford, Harvard, etc. but these are...
  35. G

    Answer: Find Moments & Reactions for Force Couple on Frame

    Homework Statement A force couple acts on the frame, which is fixed at the base. Find the moment(s) and reaction(s) at the fixed locations. Homework Equations ΣMa = 0 ΣMb = 0 ΣFy = 0 ΣFx = 0 The Attempt at a Solution Since it would be statically indeterminate, assumptions would be that the...
  36. B

    Net force =0 or Net force =GM^2/4R^2....?

    Two stars of equal mass M move with constant speed V in a circular orbital of radius R about their common center of mass .What is the net force on each star?the answer to this question was net force=GM^2/4R^2 .I want to ask that why net force not equal to zero although it is in translational...
  37. R

    Equivalent force couple systems at a point on a rigid body

    Homework Statement Attached is a pdf of the assignment problems, I'm looking at problem 1 under the "Try" section. It shows a rod attached to a wall bracket on the left, with a force applied on the right side. I'm also including a link to the solution, it's under "Problem 3.83" -...
  38. V

    B Couple geometry/trigonometry questions

    I am reading Gelfand's Trigonometry. In one of the questions he asks: "We know from geometry that a circle may be drawn through the three vertices of any triangle. Find the radius of such a circle if the sides of the triangle are 6,8, and 10." My first question is, I know that if the diameter...
  39. A

    B A couple of questions on mass increase

    I found these [experimental data](https://en.wikipedia.org/wiki/Tests_of_relativistic_energy_and_momentum#Bertozzi_experiment) on mass increase. > Data of the Bertozzi experiment show close agreement with special > relativity. Kinetic energy of five electron runs: 0.5, 1, 1.5, 4.5, 15 > MeV (or...
  40. P

    Determining the magnitude of the resultant couple

    Homework Statement Calculate the magnitude and coordinate angles of the resultant couple moment, caused by the forces. Homework Equations M= r x F The Attempt at a Solution M3= -0.2* 80k= -16k M2= 0.2* 120i= 24i M1= -0.2*100j= -20j M4= r x F= ? I just can't seem to be able to expres r into a...
  41. G

    Determine the perpendicular distance for couple

    Homework Statement two 50N are applied to the corner B and D , determine the moment of couple formed by the two forces by resolving each force into the horizontal and vertical component and adding the two resulting couples . Use the result to determine the perpendicular distance between the...
  42. demolition35

    I have a couple question I with atomic physics

    Homework Statement According to Maxwells laws of electromagnetism: If an electron spirals into the nucleus: 1. what would happen to the electron’s orbital frequency? 2. what would happen to the frequency of the emitted radiation? and 3. what kind of spectrum would be produced—a continuous or...
  43. C

    Regarding momentum transfer, couple questions.

    Hello, I've been learning calculus and physics for the last year. Let's say i have 2 point masses mass one (m1) and mass two (m2). Their respective velocity vectors are constrained to one spatial dimension, with the directional component of their velocity vectors being determined by their...
  44. D

    Preserving information/an object for a couple of billion years

    Hello guys, I have a small problem and I hope someone can help me. I have a bit of information I want to "engrave" into this planet till our sun melts it down in 4,5b years. It's not important if someone finds it, wouldn't be possible anyway, but I want it to be 'somewhere' on or in this...
  45. L

    A couple Q's about parasitic capacitance in an inductor

    First question; I was measuring capacitance in various guitar pickup coils that have the same diameter of wire with an Extech LCR Meter, and it seemed to be that the more winds, the higher the inductance as expected, but I would get lower capacitance readings, too, both at 120 kHZ and 1k Hz...
  46. S

    A Couple more "Rotation of Rigid Bodies" questions

    Homework Statement 1. It has been argued that power plants should make use of off-peak hours (such as late at night) to generate mechanical energy and store it until it is needed during peak load times, such as the middle of the day. One suggestion has been to store the energy in large...
  47. JulienB

    Proving a couple of lines do not intersect a plane in ℝ4

    Homework Statement Hi! I'm not sure the title I gave properly reflects my problem, but I did not know how to describe it in another way: (roughly translated from German) "In three dimensions, we can divide the space in two parts through a plane. In four dimensions, that does not work anymore...
  48. J

    Determine the resultant couple moment

    Homework Statement 4-70 Two couples act on the beam. If F=125 lb. determine the resultant couple moment. Homework Equations M=Fd The Attempt at a Solution I know CW is + and CCW is - ...and that is determined in the final answer, I know the solution is taking Forces times the distance...
  49. G

    Simplification of force and couple system

    Homework Statement In the figure 4-35 c , the bar is rotating at point b , but the book gave the taking moment at point b .. This is confusing... When we are taking moment at point b , the bar at particular point wouldn't move, am I right? Homework EquationsThe Attempt at a Solution
  50. I

    Optics Question -- small glass spheres to couple to fiber optic cables

    Homework Statement Homework Equations I know that yin = 0.7mm, y2 = 0mm, the index of refraction for the sphere is 1.8 and the indices of refraction for the air surrounding it is 1. The Attempt at a Solution Not sure how to even begin with the given information. I was thinking I could...
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