Tension in the rope

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Homework Statement:

What will be the tension on the rope? Suppose a rope at attached to the wall and a car and the car starts to move a velocity v in right direction.

Relevant Equations:

tension, velocity,
i believe there must be some tension while for the force to exert there must be acceleration but my intuition says different
 

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  • #2
PhanthomJay
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Why do you expect no tension in the rope? There can exist tension in the rope without accceleration . Please clarify your thoughts on this.
 
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@PhanthomJay But f=ma, and since there is no acceleration, how can there be tension? If there is, what is the answer to the question?

I think it is 0.
 
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PhanthomJay
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@PhanthomJay But f=ma, and since there is no acceleration, how can there be tension? If there is, what is the [answer to the question?

I think it is 0.
well , we don’t give answers, but here’s A hint: in the equation f= ma, f is the net force acting on the rope. So if a is 0, net force is zero, and if the car is pulling with a force on the rope, there must be another force acting on the rope to give a net force of 0. What is it? Surely you’ve seen a vehicle trying to pull another out of the mud, and neither vehicle is moving in spite of the first one with pedal to the floor, and the rope is pretty tight , right?
 
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  • #5
haruspex
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Problem Statement: What will be the tension on the rope? Suppose a rope at attached to the wall and a car and the car starts to move a velocity v in right direction.
This description is most unclear.
since there is no acceleration
Does the car suddenly go from stationary to speed v? How does it "start to move" with no acceleration?
Is the rope already taut or does it start slack?
 
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This description is most unclear.

Does the car suddenly go from stationary to speed v? How does it "start to move" with no acceleration?
Is the rope already taut or does it start slack?
I have no idea how it starts. I didn't start the thread @sumitsumit did. Honestly I am more confused by what @PhanthomJay said.
 
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haruspex
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I have no idea how it starts. I didn't start the thread @sumitsumit did. Honestly I am more confused by what @PhanthomJay said.
The correct equation is Σf=ma, i.e. the acceleration results from the sum of all forces. The tension in the rope is only one force on the car; there may be others.
 
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PhanthomJay
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I have no idea how it starts. I didn't start the thread @sumitsumit did. Honestly I am more confused by what @PhanthomJay said.
Well perhaps here is a better example...a game of ‘tug of war’. Your team is pulling on one end of the rope, trying to move the opposing team. And the opposing team is pulling the rope on the other end, trying to move your team. But assume strengths and foot holds of each team are the same, so no one is going anywhere. It’s a stalemate. There is no acceleration. Now you are trying to tell me there is no tension in the rope? There is a lot of tension , the rope might be close to breaking if it’s not strong enough. Think about Newton’s first law and draw a free body diagram of the rope from one end to an imaginary cut in-the center.
 
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  • #9
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Well perhaps here is a better example...a game of ‘tug of war’. Your team is pulling on one end of the rope, trying to move the opposing team. And the opposing team is pulling the rope on the other end, trying to move your team. But assume strengths and foot holds of each team are the same, so no one is going anywhere. It’s a stalemate. There is no acceleration. Now you are trying to tell me there is no tension in the rope? There is a lot of tension , the rope might be close to breaking if it’s not strong enough. Think about Newton’s first law and draw a free body diagram of the rope from one end to an imaginary cut in-the center.
Now I get it. Thanks!
 
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  • #10
hilbert2
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And also, if you think of the rope as consisting of a large number of really short segments that are connected to the segment before and after them, then each such segment experiences the same but opposite force from both directions if there is no acceleration.

Then there is the concept of stress, which is tension divided by cross-sectional area and therefore has units of pressure and can vary along the rope if it's not equally thick everywhere.
 
  • #11
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@PhanthomJay But f=ma, and since there is no acceleration, how can there be tension? If there is, what is the answer to the question?

I think it is 0.
Please tell me that you believe that you can’t have a force without acceleration.
 

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