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. F

    A couple of projectile trajectory-related questions

    First one (to check with others on whether or not it's correct, although I'm sure it's very easy) Homework Statement A vector makes an angle, theta, with the horizontal. The horizontal and vertical components of the vector will be equal in magnitude if angle theta is Four Choices (1) 30...
  2. R

    A couple Force, work, KE, and spring problems I'm working on.

    I'm real rusty on my physics, but here are five simple sample problems we were given, I'd appreciate your help in helping me solve these. Thanks! Homework Statement (1) A single horizontal 10.0 N force, F acts on a 2.0 kg block which is initially at rest at x=0 m. In response to the force...
  3. J

    Why is the equivalent force-couple system at corner D needed?

    Homework Statement A 63lb force F and 560lb in couple M are applied to corner A of the block shown. Replace the given force-couple system with an equivalent force-couple system at corner DHomework Equations The Attempt at a Solution I actually solved the problem but I had to guess and check. I...
  4. H

    Finding the magnitude of a couple

    Homework Statement The 140-lb uniform steel plate ABCD is welded to shaft EF and is maintained in the position shown by the couple M. Knowing that collars prevent the shaft from sliding in the bearings and that the shaft lies in the yz plane, plot the magnitude M of the couple as a function...
  5. M

    Couple Calculus Problems (Mostly Solid Revolutions)

    1. Find the vol. of a solid generated by revolving the region bounded by y = 0 and = \frac {1}{\sqrt {x}} for 1 \le x \le 2 about the line y = - 1 2. Find the volume of the solid generated by revolving the region bounded by the lines x=0, y = 0, x = 1, and the curve y = e^{x^{2}}. about the y...
  6. P

    Couple of Bounce Questions Regarding Black Holes / Universe

    I've been fascinated by the posts and discussions here about "The Bounce" that seems to be emerging from some LQG models (thanks Marcus and others). I have a couple of questions, which I don't think I've seen in posts here (my apologies if they've been raised and discussed and I've missed it)...
  7. K

    Solve Homework Questions: Moon Walk, Slingshot, Ball on String

    Homework Statement Question 1:During a walk on the Moon, an astronaut accidentally drops his camera over a 13.8 m cliff. It leaves his hands with zero speed, and after 2.2 s it has attained a velocity of 3.3 m/s downward. How far has the camera fallen after 3.9 s? Question 2: A stone is...
  8. R

    Couple of complex number questions

    Homework Statement 1)If either |z|=1 or |w|=1,prove that |\frac{z-w}{1-\overline{z}w}|=1 2)If z1,2,3, are complex numbers and \frac{z_2 - z_1}{z_3 -z_1}=\frac{z_1 -z_3}{z_2-z_3} Show that |z2-z1|=|z3-z1|=|z2-z_3| 3) Find the sum of the following series: nC1sinx + nC2 sin2x...
  9. L

    Couple of Physics Question dealing with momentum, force, etc

    Suppose I am pulling on a cart at a constant velocity, what is my net force. Is it zero? If I throw a baseball in the air, neglecting air resistance, what does the ball experience when it comes out your hand and before it hits the ground? does it experience it's weight and also a decreasing...
  10. P

    Double-slit experiment - a couple of questions

    Hi. I've just started learning about quantum mechanics, and I find the whole subject very interesting. I have read about the double-slit experiment, and I didn't understand a couple of things. Assuming one were to fire one particle at a time at the diffraction slit: - will all particles pass...
  11. T

    Equivalent Force couple to single resultant

    I have reduced the problem involving different forces and a couple in a 2D plane to an equivalent force-couple system. The force F is -27.5lbi + 11.65lbj, and the couple is -66.8inlbk. I need the single offset resultant that accounts for the couple. The way I thought to solve it was to take...
  12. N

    Bachelor's in Physics: Employability and Prospects

    I have a couple of questions. Currently I'm a second year Mechatronics Engineering student at the University of Waterloo in Canada and I'm doing horrible. It's the more technical courses that are constantly screwing me up so I've decided to switch into physics. Now I've read the "So you want to...
  13. F

    Couple Kinematics/Vectors Questions

    Hello everyone, I have couple of online homework questions and I am not asking anyone to help me do the work. I will post the question and my answers to them and I would just like someone to verify if the answer is indeed correct because I only have one chance to submit my homework...
  14. P

    Medical A couple of bothering questions

    A couple of bothering questions! Alright docs, I've got the following couple of questions: 1- Is there any way (symptoms etc.) to judge whether a person masturbates or not? 2- I have a problem that one side of my body is different from other side. Is like this that one side of my body is...
  15. E

    Solving g(x, n) and Finding Integers in f(x)

    Is there a better way to write this: g(x, n) = D(\frac{x}{n})*(n) Where D(h), unless already a decimal, expands h into a sum of its places i.e. 47=40+7, then subtracts all of the terms that are greater than or equal to one. Also, if I have a function, say f(x) = \sqrt{x}, and I only...
  16. G

    A couple of question regarding tension and Newton's laws

    1. A led cylinder hangs on a string. By another string, another cylinder is hung on the previous cylinder. If you pull fast enough, the lower string tears, if you pull slowly, the upper one tears. How does one explain this? I tried to explain this with the help of Newton's second law, but I...
  17. T

    Solving River Crossing: Angle for Boat Rowing Across River

    Homework Statement A person in a rowboat crosses a river which flows with 2.147 km/hr. The person rows with maximum velocity of 6.835 km/hr relative to the water (measured while rowing on a still lake) and wants to reach the opposite shore directly across from the start point - along a line at...
  18. A

    Can photon couple to scalar field?

    I have seen in one paper that photon is coupled to dilaton field which is scalar and motivated by string theory. I do not understand this. Photon is carrier of electromagnetic field and so I thought it can only couple to electrically charged fields. Can anyone explain?
  19. K

    Half equation for S2O32-/S4O62- couple

    I need to write the half equation for the S2O32-/S4O62- redox couple but I'm having trouble because they have the same ioic value. I've come up wth two solutions but am happy with nether... S2O32- + 3H2O + S2= S4O62- + 6H+ + 6e- or 2S2O32- = S4O62- + 2e- I know that the second one...
  20. O

    Couple of Proofs (Regular Induction / Well Ordering)

    [SOLVED] Couple of Proofs (Regular Induction / Well Ordering) Hi there everyone, I've been having a bit of trouble of solving these questions, so any help would be greatly appreciated: Homework Statement 1: Prove, via regular induction, that it is possible to draw a line-segment of length...
  21. I

    Can someone elp me with a couple of homework questions im having trouble with

    Homework Statement A hunter aims directly at a target (on the same level) 54.08m away. If the bullet leaves the gun at a speed of 143.91 m/s then at what angle should the gun be aimed in order to hit the target? (answer in radians) Homework Equations The Attempt at a Solution Vx =...
  22. R

    A couple is two forces acting in parallel

    http://users.on.net/~rohanlal/Q20.jpg A couple is two forces acting in parallel and opposite directions. F1=20N F2=22N F3-18N Couple=15N I have to determine the magnitude and direction of a single force that has the same effect on the beam as F1+F2+F3+ the couple. To do this would I find...
  23. N

    Medical Questions About Common Health Issues and Treatments

    I am new at this but i want to make sure i know what i am talking about I have researched all of these things but i am not getting a straight answer so i came you 1. When you get sick(common cold/virus) what happens? Does virus go into each cell and take its nutrients. Then after that does it...
  24. I

    Making A Small Roller Coaster - A couple of questions (please answer )

    *****Making A Small Roller Coaster - A couple of questions (please answer ASAP)***** Hi I am going to make a small roller coaster and I had a couple of questions about it. 1) What materials are the best in making different parts of a roller coaster model? (The tracks, Loops, Base and ...)...
  25. M

    Couple of questions Please help Point particle orbiting two charges

    Homework Statement Two Point particles with charge +Q lie on the z axis at z=+d/2 and z= -d/2 a point particle with charge -Q and Mass=m is orbiting in the X-Y plane in a circular radius=r the path of the orbit is thus z=0, x^2+y^2=r^2 A. find the total coulomb force on the positive...
  26. S

    Solving Couple of Problems - Help Appreciated

    Hi guys new user seeking help with couple of problems. If anyone can help that would be very much appretiated. Thanks. 1) A 1400 car traveling at a speed of 43.0 skids to a halt on wet concrete where = 0.530. How long are the skid marks? 2) A truck is parked on a slope. How big...
  27. F

    Couple of Linear Algebra Questions

    Howdy, First off, a stupid question: Why does linear indipendance not imply orthogonality? i mean we define the latter such that the inner product is zero i sort of see it as a case of the chicken and the egg, are we using two things to define each other in a cyclical way? Also what extra...
  28. R

    Couple of problems left over from Chem homework I didn't get.

    Hi, I'm taking AP Chem this year, and we just had this big assignment. I got through most of it, but here's some I need a walkthrough with. Homework Statement A titration is done using .1302M NaOH to determine the molecular weight of an acid. The acid contains one acidic hydrogen per molecule...
  29. R

    How Do Pulleys and Tensions Affect Masses and Forces?

    Homework Statement In the drawing, the rope and the pulleys are massless, and there is no friction. (m1 = 8.4 kg, and m2 = 2.95 kg.) (a) Find the tension in the rope. (b) Find the acceleration of the 8.4-kg block. (Hint: The larger mass moves twice as far as the smaller mass.)...
  30. S

    Solving for Time in Uniform Circular Motion and Moving Sidewalk Problems

    Homework Statement A centripetal-acceleration addict rides in uniform circular motion with period T = 3.58 s and radius r = 3.00 m. At one instant his acceleration is a = (7.00 m/s2)i + (-6.00 m/s2)j. At that instant, what are the following values? I found r x a to be 0 m^2/s^2 which is...
  31. S

    Hi, I'm new and have a couple questions.

    Don't think me silly, but the first question is, where do excess neutrons go? If I do a fission reaction and get protons they are just ionized hydrogen atoms, a free electron is just a negative charge to find a free proton somewhere. But since a neutron can't get back in a nucleus, where does...
  32. Evo

    Nevada couple blame Internet for neglect

    http://news.yahoo.com/s/ap/20070716/ap_on_re_us/neglect_internet_addiction They're blaming the internet, not their own idiocy and lack of self control.
  33. B

    Force and a couple other problems

    Problem 1: Calculate the normal force exerted on a 2.84 kg book resting on a surface inclined at 32.9° above the horizontal. I figure u have to use 9.8 m/s but where does the 32.9 deg come into play? Problem 2: The coefficient of static friction between a block and a horizontal floor is...
  34. R

    Force Couple Problem (Thrust of Ship)

    I am having difficulty in understanding the solution to the problem described below and illustrated by a rather crude Paint sketch I made: “Each propeller of the twin-screw ship develops a full-speed thrust of 600kN. In maneuvering the ship one propeller is turning full speed ahead and the...
  35. Y

    What is the Laplace inverse of F(s) = [3*e^(-4s)] / [s*(s^2 + s + 5/4)]?

    Homework Statement just a small part of a large problem ><a I am not even sure if this is in the right place. the first two questions i have to ask are really minor so i didnt want to make separate threads for each one. the third one is an actual problem itself tho. (1) i need the laplace...
  36. M

    Measuring Functions in L2: Closed, Bounded, and Not Compact?

    Forgive the lack of TeX. I'm too lazy to type it out right now. For reference, these are problems 13 and 14 in chapter 11 of Rudin's Principles of Mathematical Analysis, slightly reworded for lack of pretty mathematical symbols. Homework Statement Problem one: I need to show that the...
  37. F

    How Did Quantum Fluctuations Initiate the Big Bang?

    Hello everyone, can someone clear up these Big Bang problems for me? As far as I know quantum physics is a set of physical laws and rules describing our universe. If so, how can we say the Big Bang sprang from a quantum fluctuation if there was no Universe (and hence no laws of quantum...
  38. F

    A couple resistance/power problems

    Homework Statement http://www.webassign.net/pse/p28-09alt.gif" We're suppose to find the current on the R resistor(32 ohms) and then find the potential difference between point a and b. The attempt at a solution For the first problem I'm having a little problem getting this started. I tried...
  39. B

    How Do You Calculate the Couple in a Force-Couple System at Point O?

    Homework Statement I've attached an image. The question states: Replace the three forces shown, with an equivalent force-couple system at point O(origin). I've got a little ways, but I am stuck at the couple. I don't know how to use the distance in the couple. Need to know what...
  40. D

    Couple of integrals questions (and with limits)

    Homework Statement a) integral of e^(x^2) (ie, integral of e to the x squared power) b) integral from -1 to 6 of the square root of 3 plus the absolute power of x (sorry i don't know how to make it look nice on these forums...havent learned the code for it yet) c) this one is...
  41. B

    Resultant Couple and direction angle

    Homework Statement Ok, I have 3 couples applied to a bent bar. The axis is with the z going up, y left and right, and the x basically out of the page(or kinda to the left a bit). The pipe goes 28in to the right(on y axis), where the pic show a 100lb force pointing down from the +z...
  42. G01

    Another Quick Couple of Infinite Well Questions

    Homework Statement Problem 1. If I had a wavefunction: \Psi(x,0) = A(\psi_1(x) + \psi_2(x)) What is the probability of getting E1 or E2 as your energy? Problem 2 You have a wavefunction: \Psi(x,0) = Ax; 0<= x <= a/2 ; A(a-x); a/2<= x <= a What is the probability that an energy...
  43. L

    So I started my REU a couple days ago

    So I started my REU a couple days ago... I will be working on growing Aluminum Nitride wide bandgap semiconductors by molecular beam epitaxy. I am not sure what my specific project will be yet sicne I just started. My advisor has had me read a textbook on MBE technology, and he had me read up...
  44. dontdisturbmycircles

    Solve the Puzzle: Couple of Puzzles #1 & #2

    Number 1 A guy who likes watching trains enjoys walking to a nearby railroad track to wait for a train to go by. Every time, upon his return, he makes a note of whether the one he saw was a passenger train or a freight train. Over the years, his figures show that 90 per cent of the trains have...
  45. F

    Couple More Questions on Electrostatics

    Homework Statement 1) From the observation that there's an electrostatic attraction between object A and B, what's the most you can conclude about the electric charge on A and B? 2) A plastic sphere with a positive charge of 4.8E-19 C is held stationary in a gravitational field of strength...
  46. G

    A couple of problems on motion and force

    Homework Statement A flatbed truck is carrying a 3200-kg crate of heavy machinery. If the coefficient of static friction between the create and the bed of the truck is 0.65, what is the maximum rate at which the driver can decelerate when coming to a stop in order to avoid crushing the cab...
  47. S

    Schools Sooo I'm gonna graduate in May, I've started a couple of grad school apps

    but I don't have any research experience, my GPA is decent but I'm sure it'd be over a 3.5 at least by the time I'm actually done next semester, and a couple of professors seem interested in letting me do research and stuff for them the next semester or so would it be worth it to hold off the...
  48. M

    Hi can someone me with couple of my lab questions .

    Homework Statement k so we are doing a lab on determining the chemical formula of a hydrate (CuSO4.xH20) wat i need help on is these following questions: 1. suppose the hydrate was heated too quickly and some of it was lost as it spattered out of the container explain how this would affect...
  49. C

    Force Couple System: Mechanics Problems & Practical Examples

    In mechanics problems why always the force systems are replaced by force and couple systems. any practical example is available?
  50. L

    I'm New And I Have A Couple Questions For Grade 12 Physics

    okay so here's the question...can anyone figure it out... the question is... Sound with a frequency of 442 Hz. travels through steel. A wavelength of 11.66 m is measured. Find the speed of the sound in steel. Please help...i really need some direction
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