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. S

    Applying to Bachelor in Physics: Should I Stay or Go?

    I have applied to a physics program (bachelor) at a university where i live. The program is "open", there are no grade limitations (it's the same most places in Norway - studying science is not that popular). But as far as I've understood, the university is good. They have exchange programs...
  2. F

    Couple of electromagnetics questions

    E = 15 i - 8 k at a point on a conductor surface, what is the surface charge density at that point? assume Eo. surface charge density is just -Eo*E correct? but i take the magnitude of the electric field and than multiply it by Eo. am i right?
  3. T

    A couple of electric potential theory problems

    A couple of electric potential "theory" problems OK, so let's say Person A is on Planet A, where the ground potential is 1,000,000 V. Person A touches an object insulated from ground at a potential of 1,000,001 V. Person B is on Planet B, where the ground potential is 0 V. Person B touches...
  4. F

    Im stuck in a couple electromagnetics problems

    i have been at this time since 2 this afternoon, and I've only got 3 of 8 problems completely done. i need to get these done before i go insane. heres the first: plane x+2y=5 carries charge Ps = 6nC/m^2. determine E at (-1,0,1) okay, this is obviously a surface charge problem. and E =...
  5. M

    A couple of questions regarding AREAS (and getting the formulas,etc.)

    OK this problem has been giving me nonstop headaches and nightmares for over 4 days! :cry: I just can't seem to understand something here! :frown: Here's the actual problem: Suppose that you have 80 feet of fence to enclose a garden. For each garden design below, find the dimensions...
  6. P

    Proving Inverses Exist in Finite Fields: A Common Challenge in Field Theory

    First the easy one (I think): Show that x4-22x3+1 is irreducable (is that how it's spelled?) over Q. Now the one that's giving me a headache: Suppose E/F, when [E:F]=2, and char(E)>2. Prove that there exists u in E, s.t. E=F(u), when u is a root of p(x)=x^2-a, for a in F. Tried all...
  7. U

    A couple of basic physics problems

    a couple of "basic" physics problems i am stuck on a couple of my homework problems for my "basic" physics class. any help with either of them would be greatly appreciated. 1. a window washer pulls herself up in a bucket-pulley apparatus (single massless, frictionless pulley). how hard must...
  8. T

    Circuit Potential and Voltage Calculations

    1. For http://www.pen.eiu.edu/~cuemc4/circuit.bmp picture.. Calculate the potential at point D. 2. I 15-V battery is connected to three capacitors in series. The capacitors have the following capacitances: 4.5microFarads, 12.0microFarads, and 32microFarads. Find the voltage across the...
  9. T

    Couple of quick combination questions

    For the following questions there is a club consisting of six distinct men and seven distinct women. 1. In how many ways can we select a committee of three men and four women? There are C(6,3) ways to select the men and C(7,4) ways to select the woman. For each combination of the...
  10. S

    What is the Wavelength of Neutrons at Room Temperature?

    Hey, this is my first week in Quantum class, going pretty well so far. My first questoin is: 1.) What is an eV a Unit of...give it in terms of MKS Well my answer is that it is a unit of energy, and for MKS... 1 Electron*Volt = Joules 1 electron has a charge of 1.602*10^-19 C 1...
  11. J

    Solving Liquid Problems: Calculating Forces and Height Differences

    First Problem ---------------- A flat plate moves normally toward a discharging jet of water at the rate of 3 m/s. The jet discharges water at the rate of .1 m^3/s and at a speed of 18 m/s. (A) Find the force on the plate due to the jet. (B) Compare it with if the plate were stationary...
  12. S

    A couple waves questions that my class can't get

    A mass of 0.39 kg connected to a light spring with a spring constant of 22.2 N/m oscillates on a frictionless horizontal surface. If the spring is compressed 4.0 cm and released from rest, determine the following. (a) the maximum speed of the mass (b) the speed of the mass when the spring...
  13. Z

    Thinking About Quotes: Exploring Different Meanings

    I've been thinking about the following few quotes, and each time, it reminds me of how many different ways one's thoughts can be processed. I'll give my thoughts... what do you guys think about them? "Sometimes I wonder, what's the reason why... we long for someone to embrace and say hello to...
  14. A

    How Does Physics Explain These Real-World Scenarios?

    Boredom... I'm just plain stupid... (Don't know which equations to use...) If a 256 kg spacecraft weights 436 Newtons when it is on the moon, what is the gravitational field strength (in N/kg) there? To slide a 9.0 kg object at constant speed along the ground requires a force of...
  15. D

    Taylor series exp. & a couple of other questions

    Problem Find the sum of the series s(x) = \sum _{n=1} ^{\infty} \frac{1}{2^{n}} \tan \frac{x}{2^n} Solution If s(x) = \sum _{n=1} ^{\infty} \frac{1}{2^{n}} \tan \frac{x}{2^n} = \frac{x}{3} + \frac{x^3}{45} + \frac{2x^5}{945} + \dotsb \cot x = \frac{1}{x} - \frac{x}{3} -...
  16. J

    Couple of pretty simple liquid q's

    1) First ones just I am curious about what's the relationship between the velocity of a liquid being projected, like out of a hose, vertically and the height it goes. 2) An actual problem: A cylindrical tank .9 m in radius rests atop a platform 6 m high. Initially the tank is filled with...
  17. M

    A couple of questions on Gas/Steam turbines.

    1. Why Gas turbines are placed in open atmosphere while steam turbines under roof in Combined Cycle Power Plant? 2. What are the reasons for not using the reciprocating compressors with Gas turbines other than mass flow rate? Thanks in advance!
  18. T

    Solving Windows XP Login & CPU Usage Issues

    1.) I use dial-up to get online. Windows is supposed to remember my logon name and password. It has no problem with the name, but the password it gives has twice as many letters as the correct one. I assume it is giving the password twice. No matter how many times I change the password, or make...
  19. A

    Ok, need a little help in a couple of areas (2nd order w/forcing terms)

    1) For one question, the forcing term is 8cos2x - 4sinx. I am trying to solve by the method of undetermined coefficients. The solution to the homogeneous equation is c1cosx + c2sinx so for the particular solution I was using : Acos2x + Bsin2x + Cxcosx + Dxsinx, where I added the x's into the...
  20. T

    A couple of questions of acetic acid

    Had a lab few days ago and a question was presented: Some people claim that women possesses better color vision than men. Suppose ths is true. Two people perform this experiment and their results are as follows: Student1: Acetic Acid Concentration - 4.5% Student2: Acetic Acid...
  21. B

    Solving Questions on f(x) = x^2 + x and x/|x| at x=0

    I kinda have a question and an answer check... well here's my check. Let f(x) = x^2 + x. For any readl number a, let Ty be the y-intrecept of the tangent line to f(a), let Nx and Ny be, respectivly, the x-intercept and y-intercepts of the normal line to f(a). SHow that a = 0 is the only value...
  22. H

    How Do You Solve Complex Pulley System Problems in Physics?

    HELP! pulley problems, can't figure formula out... ok, for physics here at uf, there are 2 problems in this homework i just can't figure out, and I am sure I am just being stupid, but can anyone help me? here they are... In Figure 5-50, three ballot boxes are connected by cords, one of which...
  23. J

    How Fast Must a Limo Travel Near Light Speed to Appear Shorter?

    hey everyone I'm new here. you all seem great at physics and my teacher gave us these problems and i have no clue as to how to do them! please help me it is due tonight! 1.Natalie designs stretch limo that is 9 m long but appears to be only 5.000m long when driven at speeds near the speed of...
  24. Nebula

    How Do You Solve These Blackbody Radiation Problems?

    A couple Blackbody Problems? I'm a little confused about these two problems involving blackbodies, hopefully someone could give me a bit of insight. Thanks in advance. 1. For a blackbody we there is a frequency peak and a wavelennght peak. Let's call em v and w respectively. Now consider the...
  25. A

    A couple of groovy avatar type pictures I made

    I was bored and started playing with little pictures using Japanese stuff: http://bad-sports.com/~archive/images/avatar.gif http://bad-sports.com/~archive/images/yinyang.gif
  26. F

    I have a couple of brain blocks.

    I've got a U-tube filled with Mercury and water. If I add 11.2 cm of water to the left side, how much does the mercury rise on the right side? For simplicity's sake, D will stand for density, p0 for initial pressure, w = water, m = mercury, h = 11.2 cm for the water and d = the distance the...
  27. Z

    What is the Proof for the Sum of Natural Numbers to n and the Derivative of x^n?

    I'm writing up my maths notes to the computer, while looking over maths notes for series I spotted another way of proving the sum of natural numbers to n (to what I've been taught). By definition: \sum_{k=1}^n k = n + (n-1) + (n-2) + \ldots + (n - [n-2]) + (n - [n-1]) Separating terms...
  28. A

    What Calculations Are Needed to Achieve Equilibrium in These Statics Problems?

    Hi, I have a couple of questions from a statics assignment that I'm in need of help on. Here's what I have so far: http://216.170.11.226/pub/6131.jpg Two rods are connected by a slider block as shown. Neglecting the effect of friction, determine the couple Ma required to hold the system...
  29. E

    A couple of Questions can someone help me?

    Ok I need help with this questions.. would someone be kind enough to honestly answer them? It's a project and I need at least 25 years between two individuals, same questions for the two. I need people older than 21 =-/ and it would really help if I could get at least 1/2 a page typed...
  30. B

    Help with Couple of Calculus Problems

    Hello, I am completely stumped by some of these problems, and have no where else to get help, can anyone help me with these problems? Any help would be greatly appreciated. Thank you very much. 1. The function v(t)=12t(squared) - 16t is the velocity in m/sec of a particle moving along the...
  31. M

    A couple pretty easy integration problems im stuck on

    integral of 10/((x-1)(x^2+9)) dx integral of x^3/((x+1)^3) dx both these are under the partial fraction section, so using those methods would be helpful... thanks!
  32. P

    How Do You Solve These Kinematics Problems Involving Falling Objects?

    Can anyone suggest how to do these problems. 1) A rocks is dropped from a sea cliff and the sound of it striking the ocean is heard 3.4s later. If the speed of sound is 340m/s, how high is the cliff? 2) An apple is dropped and a multi-flash camera is used to take photographs of the...
  33. J

    Help with a couple of questions

    1. What is (integral over all space) delta^3(r-r0)r^2d^3r where d^3r=dxdydz=dV and r0=(0,1,2)? answer: I'm not quite sure what the intergral over all space means.How can r0 be integrated if it's just given as points? 2. Obtain Coulomb's law for the electric field of a point charge from...
  34. Ivan Seeking

    Why should you be careful when choosing the size of a relay contact or fuse?

    Over the years I have run across a few surprising facts about electrical components. I thought to pass on a couple of these [somewhat obscure?] interesting and often important details. So here are a couple of questions to chew on. 1). Why is it bad to oversize a relay contact? In other words...
  35. J

    Understanding Vector Quantities and Projections: Answers to Common Questions

    1. Is every quantity that has three components in three dimensions a vector? From the definition of a vector I think it is. If it isn't, can you give me an example? 2. How can you tell if the projection of a force vector F along the velocity vector v of a particle is a scalar?
  36. I

    Questions About Event Horizon, Singularity & Schwarzchild Radius

    A Couple Questions... I was recently watching a t.v. show and the following terms came up: event horizon, singularity and schwarzchild radius... Can anyone tell me what these things are?
  37. N

    A couple problems with angular momentum

    I know a couple of these I already asked, but I'm really close and missing something. Could someone help?? 1) A ring of mass 2.53 kg, inner radius 6.00 cm, and outer radius 8.00 cm is rolling (without slipping) up an incline plane which makes an angle of = 36.4°. At the moment the ring is...
  38. S

    Effects from Oct 28th CME's wont hit Earth for a couple days?

    This CNN article http://www.cnn.com/TECH/space/ a big solar flare erupted today and it claims some kind of supercharged particles could hit Earth in one to two days….It talks about coronal mass ejections (CME)being associated with solar flares... I guess whatever it is that is predicted to...
  39. M

    What is the height of the tennis ball when it leaves the racket?

    Kinematics in Two dimensions, from Cutnell & Johnson Physics: A tennis ball is struck such that it leaves the racket horizontally with a speed of 28 m/s. The ball hits the court at a horizontal distance of 19.6 m from the racket. What is the height of the tenis ball when it leaves the...
  40. C

    How Accurate Are These Chemistry Calculation Methods?

    Consider this eq, It is balanced: KCN+HCl=KCl+HCN If a sample of 0.140g of KCN is treated with an excess of HCl, calculate the amount of HCN formed, in grams: I just want to know if I did this right 0.140g KCN/65g KCN = x/27g HCN and I got .058 g Another probem: Ammonium Nitrate...
  41. M

    How High Does the Flowerpot Rise and How Long Must the Runner Accelerate?

    Hey can someone help me out with one or both of these questions? 1. A dog sees a flowerpot sail up and then back down a window (height of window is 1.77m). If the total time the pot is in sight for 1.0 s, find the height above the top of the window to which the pot rises. 2. A runner...
  42. M

    Calculating Heights and Acceleration: A Physics Question

    Hey can someone help me out with one or both of these questions? 1. A dog sees a flowerpot sail up and then back down a window (height of window is 1.77m). If the total time the pot is in sight for 1.0 s, find the height above the top of the window to which the pot rises. 2. A runner...
  43. J

    How Do Reflection and Curvature Affect Images in Optics?

    1. Imagine that you are standing 5 ft from and looking directly toward, a brass ball 1 foot in diameterhanging in front of a pawn shop. Describe the image you would see in the ball. -Would I have to find the an answer that tells me that it is inverted, real, virtual, etc? 2. What formula...
  44. J

    How to Calculate Speed and Time for Pions and Spacecraft?

    1. What is the speed of a beam of pions if their average lifetime is measured to be 4.34×10-8s? At rest, their lifetime is 2.60×10-8s. - Would I use velocity= distance/time? 4.34/2.6=velocity 2. A certain star is 70.6 light-years away. How many years would it take a spacecraft traveling...
  45. A

    A couple of basic questions about electromagnetic waves

    Hi, I'm new. From what I understand, radio waves are generated these days using alternating currents or mechanically moving charges. The highest frequencies that modern technology reaches is somewhere in the bottom of infrared. Theoretically speaking, is it possible to emit visible light...
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