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Pulley, Strings, Friction [Please..]{Mechanics}

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Xin R
#1
Apr24-11, 01:27 AM
P: 8
1. The problem statement, all variables and given/known data

1) I am really confused about how tension is same on both sides of pulley. Also, how do friction of pulley affect tension in string?

2) Also want to know how tension provides torque to pulley since tension in each segment is perfectly cancelled out by adjoining string segments.

3) If possible can anyone give me free body diagram of tension in each segments of various parts in a pulley?

4) What is the basis of constrained motion? How do i use them to make relations??


2. Relevant equations

No equations. Conceptual Problem

3. The attempt at a solution

tried a lot. No use.. :(
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Xin R
#2
Apr24-11, 05:36 AM
P: 8
NOone here to clear by doubts huh??! !!!!
Doc Al
#3
Apr24-11, 05:52 AM
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Quote Quote by Xin R View Post
1) I am really confused about how tension is same on both sides of pulley. Also, how do friction of pulley affect tension in string?
Tension is the same on both sides of a massless and frictionless pulley.

2) Also want to know how tension provides torque to pulley since tension in each segment is perfectly cancelled out by adjoining string segments.
I don't understand what you mean 'tension in each segment being canceled out'. For a segment of a massless rope, the net force is zero. But the rope still transmits a force from one end to the other.

Xin R
#4
Apr24-11, 06:18 AM
P: 8
Pulley, Strings, Friction [Please..]{Mechanics}

Quote Quote by Doc Al View Post
Tension is the same on both sides of a massless and frictionless pulley.


I don't understand what you mean 'tension in each segment being canceled out'. For a segment of a massless rope, the net force is zero. But the rope still transmits a force from one end to the other.
How?!! How does tension change if there is friction and mass on pulley?
Doc Al
#5
Apr24-11, 06:23 AM
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Quote Quote by Xin R View Post
How?!! How does tension change if there is friction and mass on pulley?
Well, something's got to accelerate the massive pulley or overcome the friction. If the tension were the same on both sides, there would be no net torque.
Xin R
#6
Apr24-11, 06:28 AM
P: 8
Quote Quote by Doc Al View Post
Well, something's got to accelerate the massive pulley or overcome the friction. If the tension were the same on both sides, there would be no net torque.
Okay. Consider this. There is a slit through which the string passes and slit provides friction. is tension same on both sides of pulley? Is tension same on both sides of slit?


Consider this. there is no block on one side of pulley. Is there tension on string now?
What is providing centripetal acceleration required by string to move in circular path??


Consider this: There is two blocks on one side of a pulley, connected in series and one block on other side. is tension same on both sides of pulley and between the two blocks on one side?
You have cleared a majour part of my doubt . Thanks!
Doc Al
#7
Apr24-11, 06:36 AM
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Quote Quote by Xin R View Post
Okay. Consider this. There is a slit through which the string passes and slit provides friction. is tension same on both sides of pulley? Is tension same on both sides of slit?
Sorry, but I don't understand what you mean.

Consider this. there is no block on one side of pulley. Is there tension on string now?
If I understand you correctly, no.
What is providing centripetal acceleration required by string to move in circular path??
The string is treated as massless.

Consider this: There is two blocks on one side of a pulley, connected in series and one block on other side. is tension same on both sides of pulley
Yes, if the pulley is massless and frictionless.
and between the two blocks on one side?
No. The rope segment between those two blocks will have a different tension than the other rope segment.
Xin R
#8
Apr24-11, 06:45 AM
P: 8
Quote Quote by Doc Al View Post
Sorry, but I don't understand what you mean.


Thanks!

If tension is different, how do i calculate that?
If I understand you correctly, no.
May i Know Why? What is the purpose of tension afterall?

The string is treated as massless.
I got you.


Yes, if the pulley is massless and frictionless.
I got you


No. The rope segment between those two blocks will have a different tension than the other rope segment.
How do i calculate that tension??


Thanks a lot.
Doc Al
#9
Apr24-11, 06:48 AM
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Quote Quote by Xin R View Post
May i Know Why? What is the purpose of tension afterall?
A massless rope requires something pulling on each end for it to have tension.

How do i calculate that tension??
In the usual manner: Identify the forces acting on each body and apply Newton's 2nd law.
Xin R
#10
Apr24-11, 07:03 AM
P: 8
Thanks but answer the first question also?
Doc Al
#11
Apr24-11, 07:05 AM
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Quote Quote by Xin R View Post
Thanks but answer the first question also?
About the slit? If it provides friction, then the tension will be different on each side of the slit.
Xin R
#12
Apr24-11, 07:11 AM
P: 8
Can you please explain how?
Doc Al
#13
Apr24-11, 07:15 AM
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Quote Quote by Xin R View Post
Can you please explain how?
How much friction does the slit exert?
Xin R
#14
Apr24-11, 07:20 AM
P: 8
10N. Or take it as unknown if you want it that way.
Doc Al
#15
Apr24-11, 07:23 AM
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Quote Quote by Xin R View Post
10N. Or take it as unknown if you want it that way.
If the force required to overcome friction is 10N, then that's the difference in tension across the slit.


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