Tension When Moving String w/ Object Attached

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Discussion Overview

The discussion revolves around the concept of tension in a string when an object is attached and the string is moved upward. Participants explore the relationship between the force exerted on the string and the resulting tension, considering Newton's laws of motion.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant states that when an object is held still, the tension in the string equals the weight of the object.
  • Another participant argues that to accelerate the object upward, the tension in the string must be increased, referencing Newton's 2nd law.
  • A participant points out that moving upward implies acceleration, which increases tension due to the opposing force of gravity.
  • There is a suggestion that if the upward force applied to the string is 2N, the tension increases by 2N, referencing Newton's 3rd law.
  • Some participants assert that the force exerted on the string directly corresponds to the tension, treating the string as massless.
  • A question arises about whether the tension is the equal and opposite reaction to the force applied to the string, to which another participant agrees.

Areas of Agreement / Disagreement

Participants generally agree that the tension in the string increases with the force applied to it, but there are nuances regarding the implications of Newton's laws and the conditions under which these statements hold true. The discussion remains somewhat unresolved regarding the precise relationship between the forces and tension in different scenarios.

Contextual Notes

Some assumptions are made regarding the mass of the string and the conditions under which the forces are applied. The discussion does not fully resolve the implications of these assumptions on the tension calculations.

johnathon
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If I attach an object to the end of a string and hold it still I get that the tension will be equal to the weight of the object. But what if I start to move the string up. How does that affect the tension?
 
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In order to accelerate the object upward you must increase the tension in the string. (Analyze the forces acting on the object and apply Newton's 2nd law.)
 
Moving upward means accelerating upward right? If so then gravity is pulling down and you are pulling up and thus string tension is increased. If you accelerate upward fast enough you could break the string in which case tension returns to zero
 
Doc Al said:
In order to accelerate the object upward you must increase the tension in the string. (Analyze the forces acting on the object and apply Newton's 2nd law.)

So if I lift up the string with a force of 2N, the tension also increases by 2N (applying Newton's 3rd law)?
 
Last edited:
johnathon said:
So if I lift up the string with a force of 2N, the tension also increases by 2N?
Whatever force you exert on the string is the string tension.

If you increase the force you pull up on the string by 2N, then the tension must increase by 2N. (Treating the string as massless.)
 
Doc Al said:
Whatever force you exert on the string is the string tension.

If you increase the force you pull up on the string by 2N, then the tension must increase by 2N. (Treating the string as massless.)
So is the tension the equal and opposite reaction to my pulling?
 
johnathon said:
So is the tension the equal and opposite reaction to my pulling?
Exactly.
 
Doc Al said:
Exactly.

Ah, brilliant. Thanks
 

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