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Calculate tension in a rope 
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#1
Nov2311, 01:18 PM

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Hi,
I'm a bit confused with determining the tension in a rope. For example, when two people are puling on a rope, one with a force F and the other with a force 2F, how can you calculate the tension? I know the tension at any point in a rope is the magnitude of force acting at that point, and that the tension is the same everywhere if the rope is in equilibrum. But I can't figure out what to do next.. I hope someone can help me, since I'm kind of stuck on every physics problem involving tension.. 


#2
Nov2311, 01:36 PM

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#3
Nov2311, 01:41 PM

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If one person is pulling with a force F and the other is pulling on the same rope with 2F in the opposite direction then would not the whole thing would accelerate by a resultant force of F in the direction of 2F?



#4
Nov2311, 01:47 PM

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Calculate tension in a rope
But I doubt that that's what the OP has in mind. 


#5
Nov2311, 03:34 PM

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F_{net} = maIf an object has either (1) negligible mass, or (2) constant or zero velocity (a=0), then the net force must be zero. 


#6
Nov2311, 03:56 PM

P: 3

Thank you for all your replies, I see my F2F theory didn't make sence.
I still have trouble with tension though.. For example; if two people are pulling on a rope (with a force F) then how come the rope doesn't fall, since there are no upward forces to counter gravity? (excuse me for my bad English, it's not exactly my native language). 


#7
Nov2311, 04:10 PM

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A real rope has mass and weight and would sag a bit between the two people. They would end up exerting a vertical component of force to support the weight of the rope. 


#8
Nov2411, 08:35 PM

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#9
Nov2411, 09:20 PM

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#10
Nov2511, 04:37 AM

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How long the two people could maintain such a force difference on a piece of rope is another story. Not for long. 


#11
Nov2611, 09:00 AM

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Moderator's note: I have moved a related post to a new thread in Homework & Coursework Questions:
http://www.physicsforums.com/showthread.php?t=554072 


#12
Nov2611, 04:21 PM

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#13
Nov2611, 04:29 PM

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Massless rope and a rope with mass. My cryptic message was to get someone to respond with the difference, but no luck. A massless rope is idealized so that it offers no resistance to force. A force on one end would be transmitted immediately to the other end. The tension in the rope is a constant anywhere along its length. For a real rope, with a mass, a force on one end will take some time to be felt at the other end. A change in force is not transmitted instantaneously to the other end, but travels down the rope much like a sound wave in air. That would be a fair simple description. 


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