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. M

    Help with a couple physics problems

    I am having some trouble with a couple of physics h/w problems and would appreciate any help you can give me.. Julie pulls a 61.5 N bag a distance of 278 m at a constant velocity. The force she exerts is 48.4 N at an angle of 66.8 degrees above the horizontal. I found the work julie does on...
  2. J

    What is the force in the y-direction given the force and angle?

    thanks in advance for any help
  3. T

    Conservation of Momentum in Collisions

    I have no idea how to do this first one 1. Youre coasting with a friend on a sled, going a constant velocity, having a momentum of +120kg m/s when suddenly your friend bails off the sled. Assuming there are no net external forces acting on the system which of the following gives a correct...
  4. G

    Need help with a couple of BVP's.

    I've got a couple of BVP's I'm working on that are giving me some problems. First, I'm asked to solve the 1-D Heat Equation: k \frac{\partial^2 u}{\partial x^2} = \frac{\partial u}{\partial t} in a thin rod of length L subject to the following: BC1) u(0, t) = 0 BC2) u(L, t) = 0 IC) 2...
  5. R

    Forces, Moments and couple question, Can you please check its right

    Please find the attachment below. Thanks
  6. R

    How Do Forces and Couples Work in Physics?

    Please find the attachment below. Thanks
  7. N

    Can a Moment Couple Really Impact an Entire Building Equally?

    I have been learning about moment couples and all of their greatness...but even after seeing and verifying myself the mathematical proof I just can't bring myself to fathom the fact that a moment couple acts as a 'free vector.' How can every single point on an object feel the same moment at...
  8. S

    Couple of Problems - simple integrals

    Please confirm my answers 1) definite integral 0 to 1 [1/1+x^2 + 9e^x - 1/sqrt(x)] = tan^-1(x) + 9e^x - 2x^1/2 I know that to evaluate it I just plug in b for x - a for x 2) indefinte integral sin(3t)cos(3t) = 1/3 (-cos(3t)sin(3t))dt
  9. C

    Couples Rotate Objects: Understanding Rotation Points

    when a couple acts on an object it will tend to rotate it and it will not tend to translate it But the sentence "tend to rotate" but tend to rotate about which point or axis?
  10. C

    Couple questions involving monoids/isomorphisms

    I'm having trouble with these two questions. Problem 1: Prove that the multiplicative monoid N of natural numbers 1, 2,... is a free commutative monoid. Problem 2: Is the multiplicative monoid N isomorphic to the additive monoid N_0 x N_0 x ...x N_0 (n times), for any n = 1, 2,...? Prove...
  11. S

    Electric Fields: Help Needed for Questions on Charge and Magnitude

    help needed on a couple questions - electric fields anyone able to lend a hand? 1. How many excess electrons must be added to an isolated spherical conductor of diameer 30.0 cm to produce an electric field of 1155 N/C just outside the surface? permittivity of free space and charge on an...
  12. C

    Couple of v. important problems

    there's a couple of problems that i have to give in at the end of this lunctime that i just can't work out how to approach or what formulas to use: 1. A 70g tennis ball falls 2 meters and bounces back up to a height of 1.9 meters (a)How much kinetic energy does the tennis ball have...
  13. D

    Continuous Functions and Integration: True or False?

    a) if f and g are continuous on [a,b] then: int [f(x)g(x) dx] = int [f(x) dx] * int [g(x) dx] i said false. b) if f is continuous on [a,b] then int [xf(x) dx] = x int [f(x) dx] again i said false (x isn't constant)
  14. A

    A couple of free books to download

    I am sorry if this has been posted before. I just stumbled over this link and it got me drooling:-p http://ads.harvard.edu/books/ Does anyone know if the fundamentals of stellar astrophysics by Collins is a good book?
  15. C

    Why Do Electrons Orbit Protons & Planets Orbit the Sun?

    Why don't elctrons just go and stick to the protons in the nucleus as they are opposite charged particles, why do they keep orbiting them. Another question related to this. Why don't planets just go and crash the sun due to gravity, why do they orbit around it,Who told them or set them in...
  16. A

    A couple questions - need answers to for final

    While studying for my final exam in physics I have come across some problems that I need resolved. 1) Suppose a the energy required to bring an electron in the ground state of an atom to the second energy level is X J and the energy to bring it to the third is Y J. What happens to a photon...
  17. JamesU

    Why Would Grandparents Hire a Hitman Against Their Own Family?

    http://www.foxnews.com/story/0,2933,197952,00.html these people suck...
  18. R

    Stuck on couple related rates problems

    1. A ship with a long anchor chain is anchored in 11 fathoms of water. The anchor chain is being wound in at a rate of 10 fathoms/minute, causing the ship to move toward the spot directly above the anchor resting on the seabed. The hawsehole ( the point of contact between ship and chain) is...
  19. S

    How Do You Calculate Object Fall Times with Air and Water Resistance?

    Hey folks, new guy here! I have a couple of, what I believe to be, pretty elementary physics questions. I hope you can help me adjust my formulas and help me figure this out! I have this formula for calculating how long it takes an object to fall a certain distance: Time(squared) = (2 x...
  20. V

    How do I resolve the moments into vectors and forces?

    Hi everyone. I have this problem and I don't even know how to start it! If you are familiar with my previous posts, you know that I usually have most of a problem completed before posting here with my difficulties, however, I cannot even start this one! I don't think there is enough...
  21. E

    A Couple More Simple Think critically and Explain Questions

    Think and Explain 1. Why is it important that the resistance of an extension cord be small when it is used to power an electric heater? 2. Will the current on a light bulb connected to 220V be more or less than when the same light bulb is connected to 110V? How much? 3. In 60- Hz...
  22. H

    Can someone check a couple of these?

    Are these the correct answers for the following questions? 1 Solve the Bernoulli equation. a) x\frac{dy}{dx}+67=3xy^\frac{4}{3} What I got: \frac{1}{y^\frac{1}{3}}=x+cx^2 b) x^2y'+2xy=5y^4 What I got: 2y^(-3)=\frac{30}{13}\frac{1}{x}+cx^12 2 Solve each differential...
  23. B

    Couple questions on work and conservation of energy

    1. A woman at an airport is towing her 29.0 kg suitcase at constant speed by pulling on the strap at an angle above the horizontal. She pulls on the strap with a 40.0 N force, and the friction force on the suitcase is 12.0 N. (a) What angle does the strap make with the horizontal? (b) What...
  24. W

    How Do Complex Numbers Affect Trigonometric and Quantum Mechanical Equations?

    the first one says: Prove that: a) |sin z | \geq |sin x| b) |cos z | \geq |cos x| Where I guess z = x+iy... What I have done: Well I am pretty stumped on this one, I have though about expanding sin z into (sin x) (cosh y) + (i cos x) (sinh y) . I don't think that helps me prove...
  25. A

    A couple questions on integration

    Hey everyone, I've been having a little trouble with a few HW questions. If you guys could point me in the direction (ie- help me find the method to solve) I would really appreciate it. The q's are: 1. The definite integral from 3 to 8 of- x^4(ln3x)dx For this one I am not sure wether I...
  26. E

    How to Calculate Argon Atom Energy Fractions and Reaction Rates?

    I am completely stuck on a couple of questions and would like a bit of help on these. First one. This I have no idea where to even start and I can't find anything on it in my text either. So maybe a formula or point me in the right direction would help.:biggrin: Calculate the fraction of...
  27. S

    Help me find a couple of good articles

    can you please help me find a good article on all that weird stuff in modern physics? the article can be specific or general ... it doesn't really matter as long as it pertains to modern physics
  28. M

    Quick Questions: Science Test Retake Tips and Help

    Ok so I recently took a sceience test, and it was a disaster, but he's giving us the chance to retake it. The first time through, the only thing that saved my grade was my "creative" answers (my definition for farad was: "Farad Hazim was the first Arabian telemarketer to eat his own head in...
  29. B

    A couple of angular accelaration problems

    I'm having many a woes with angular accelaration in my DE Physics class. Could you guys explain to me how to do these 3 problems. (If I can get one of them by logical deduction from the other problems don't go out of your way.) Thanks. A merry-go-round accelerating uniformly from rest...
  30. D

    How Can I Solve Complex Physics Homework Problems?

    Hi, I’m having a really difficult time in physics, and I need some help on this homework assignment. Here are the questions and the work I’ve done. I really don’t know how to approach them, and at this point, I’m just kinda throwing equations at them haphazardly… 5. A 175 kg weather...
  31. P

    Solve Physics Problems: Inclined Slide & Dart Gun Spring Compression

    1. Mass M is sliding down the inclined part of a slide at a speed of 1.93 m/s. The mass stops a distance of S2= 2.1 m along the level part of the slide. The distance S1= 1.22 m and the angle theta= 34.70 deg. Calculate the coefficient of kinetic friction for the mass on the surface. I used...
  32. L

    How Does a Cookie Jar's Motion on an Incline Relate to Physics Principles?

    1.) A cookie jar is moving up a 39.7o incline. At a point 0.56 m from the bottom of the incline (measured along the incline), it has a speed of 1.48 m/s. The coefficient of kinetic friction between the jar and incline is 0.15. (a) How much farther up the incline will the jar move? (b) How...
  33. C

    How to get mag. & angles of resultant couple moment

    I have another thread for another problem, but no one seems to be responding about this second problem, so i'll post it here. Need to find the magnitude and direction/space angles of the resultant couple moment of two valve handles being turned, as pictured...
  34. C

    What Are Some Tips for Starting Moment Couple Problems?

    Okay, having some problems figuring out how to start this problem on a moment couple: http://img347.imageshack.us/img347/6939/problem55hb.jpg And the same thing for this one: http://img347.imageshack.us/img347/2488/problem64sx.jpg Any tips on how to start each one? I think I just need...
  35. D

    Electric Fields: A couple of general questions

    I have a general question about dipoles. Doesn't the magnitude of the electric field attain its highest values in the vicinity of the midpoint of the distance between the positive and negative point charges? This is interesting, because if you consider only one point charge, then the magnitude...
  36. K

    A Couple of Conceptual Questions Need help

    Thank you. Consider a particle moving in a straight line. Does a Large change in speed always lead to a large acceleration? Explain. For a car traveling at a given speed, there is corresponding stopping distance associated with that speed. The stopping distance is the the distance the...
  37. B

    MATLAB Counting 4 Couple Table Arrangements in MATLAB

    I tried to write a function that would count all possible combinations that 4 couples could sit at a table assuming no man can sit next to his wife or next to another man. and 1wife and 1 husband sit at fixed positions. my problem doesn't compile and it says i either have too many or too few...
  38. M

    Can You Solve These Physics Problems on Constant Acceleration?

    Right now I've only learned 3 equations dealing with constant accleration v_f=v_i+a_s\Delta t s_f=s_i+v_i\Delta t+1/2a_s(\Delta t)^2 v_f^2=v_i^2+2a_s\Delta s Ok first problem: A Porsche challenges a Honda to a 400-m race. Because the Porsche's acceleration of 3.5m/s^2 is...
  39. M

    A couple of calc III, 3d drawings & sphere problems

    Hello everyone, I'm stuck on some problems, This is the first homeowrk assignment and I'm pretty lost! I'm going to list the directions and show you what I have done so far, any help would be great! Here is my work to the problems: //http://img175.imageshack.us/img175/4090/4108rz.jpg...
  40. T

    How Do You Solve These Challenging Physics Problems?

    ok this is a new subject and my teacher is just horrible, so any help will be great thanks 1. One cubic centimeter (1.0 cm3) of water has a mass of 1.0 e-3 kg. Determine the mass of 1.0 m3 of water (in kg). -I thought you would take the 1.0 e-3 kg and multiply it by 100 since you are going...
  41. V

    Calculating Personal Income Tax and Comparing Salaries

    I have a couple math questions that I am a bit rusty with. I know they are probably really easy, but bare with me, as I haven't done problems like these in a while. Here we go: A man makes $75,000. He must pay federal personal income tax of 10% on the first $12,000 of his income, 15% on...
  42. T

    Engineering Mechanics Couple system question

    what is this problem searching for? A 25-lb force acting in a vertical plane parallel to the yz plane is applied to the 8-in.-long horizontal handle AB of a socket wrench. Replace the force with an equivalent force-couple system at the origin O of the coordinate system. See attached pic...
  43. B

    How Do You Calculate Oscillation Periods and Forces on a Dam?

    Hi, I have a couple general (pretty much abstract) mechanics questions, and I'm not sure I'm going the right way about doing them. Any help would be appreciated. 1)On a flat surface with friction, you have a massless spring with a spring constant (k) attached to a wall on one end, and on the...
  44. J

    How Do I Solve These Couple Trig Problems?

    A few trig problems that require the same thing or concept. As always I appreciate the help. 1) If Tan A=1/3 and Tan B=1/2 show that Tan(1/3 + 1/2) = 1 (Tan1/2 + Tan1/3) / 1-tan(1/2)tan(1/3) I am a little confused with this because I can't use a calculator and am confused on what...
  45. M

    Quantum Numbers for a couple of electrons Help needed

    Good evening scholars! i just had a couple of questions about QNs. ok so the problem says: Give the sets of {n, l, m, s} for the electrons in: a) 4p^2 b) 6s^2 i just want to see if I'm on the right track. here's what i put for the first one (a): n= 4 l= 1 m= -1, 0 s= +/- 1/2...
  46. L

    Physics 2 exam tomorrow. Need help with a couple more problems and im good

    Physics 2 exam tomorrow. Need help with a couple more problems and I am good! :) 1. a circuit has a 137 mH inductor across AB (the whole curcuit is a square with corners ABCD), a 50 ohm resistor across BC, and a 25 uF capacitor across CD with a 115V @ 60 hz power source between DA. What is...
  47. C

    Couple questions about complex integrals

    we recently started integrals over the complex plane, in complex analysis. But, I am confused on the iterpretation of some of it. From what I've heard/understand, there Is no geometrical interpretation of a complex integral. Why is this? Also, why is it 'illegal' to do an indefinate integral...
  48. S

    Solving Torque and Power Problems with Drywall and Rotating Platforms

    1. Two builders carry a sheet of drywall up a ramp. Assume that W = 1.70 m, L = 3.20 m, = 18.0°, and that the lead builder carries a weight of 137.0 N (30.8 lb). What is the weight carried by the builder at the rear ? I know torque and all forces add up to zero, as the drywall is not...
  49. S

    Short Title: Does Einstein's Special Relativity Disprove the Existence of Ether?

    Hi to anyone reading this. This is my first thread on this site. I am enthusiastic and very interested in physics. Currently i am trying to understand the universe around me. I have a couple of questions id like to ask and if they could be answered that would be greatly appreciated. Personally...
  50. L

    Why Do Different Objects Make Different Sounds When Dropped?

    Why do two objects when dropped on the floor make different sounds? (i.e, coin and piece of wood) What's a system? and please give me an example of it demonstrating Newton's First Law of Motion. How do I calculate the speed of an object that demonstates linear motion?
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