Which string cutten? (impulse)

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    Impulse String
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Discussion Overview

The discussion revolves around a physics problem involving a metal ball hanging by two strings, where participants explore the effects of pulling the lower string quickly (impulse) versus slowly (static) and which string would break under these conditions. The scope includes theoretical reasoning, experimental observations, and mathematical modeling.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants note that the method of attachment and the lengths of the strings are undefined parameters that could affect the outcome.
  • One participant claims that pulling the lower string quickly will result in it breaking first due to the inertia of the ball, while pulling slowly will cause the upper string to break first.
  • Another participant questions the reliability of the initial claim and asks for a detailed description of the experimental setup.
  • It is suggested that if the strings are sound and of equal breaking strain, the behavior under impulse and static loads can be analyzed further.
  • One participant explains that the stress and strain dynamics differ between the two strings depending on the speed of the applied load, leading to different breaking points.
  • There are requests for mathematical explanations and formulas to support the claims regarding impulse loads and the behavior of the strings.
  • Another participant proposes modeling the strings as springs and suggests that the calculations could be manageable with the right approach.

Areas of Agreement / Disagreement

Participants express differing views on the conditions under which each string would break, with some supporting the initial claims while others seek clarification and additional details. No consensus is reached on the definitive outcome of the scenario.

Contextual Notes

Participants highlight the importance of various parameters such as string length, modulus, and the method of attachment, which remain undefined and could significantly influence the results.

Who May Find This Useful

This discussion may be of interest to those studying mechanics, material science, or anyone exploring the dynamics of forces and tension in strings or similar systems.

persia7
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suppose a metal ball is hanging by a string and there is another string is hanging at buttom of the ball if you pull buttom string very fast which of strings (up and buttom) will be cutten ?
 
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There are too many undefined parameters in your question. Method of attachment is one example thereof. I admit that I don't really have a clue about this, but it seems to me that even the lengths of the string segments would be relevant. (The longer the string is, the more likely it is to break.)
 
i know the answer, but i don't why. if you pull very fast(impulse) the buttom string cutten and if you pull slowly(static) the upper cut, but why?
 
Have you repeated this experiment often enough to be sure that the results are guaranteed? If so, will you please describe the set-up in more detail? I'm not disputing your conclusion; I just don't know exactly how you arrived at it.
 
Danger said:
There are too many undefined parameters in your question.
It is reasonable to assume the strings are sound and fit for purpose, are securely attached, and are of equal breaking strain.

It is a very good demonstration, persia7.
 
Initially the stress & strain is higher in the upper string as there is no load on the lower one.

If an impulse load is applied to the lower string then the inertia of the metal ball causes a delay between the rising stress in the lower string and rising stress in the upper string. If the impulse is short but large enough the strain in the bottom string will reach breaking point before the top. So lower string breakes first.

If the load is applied slowly then the strain increases at the same _rate_ in both strings BUT the top string had a head start so it reaches breaking point first. Upper string breakes first.
 
i agree with CWatters , but can you explain with formula what happen when impulse load applied on lower string?
 
persia7 said:
i agree with CWatters , but can you explain with formula what happen when impulse load applied on lower string?

For a brief but strong tug, the ball might as well be a brick wall. You yank on a string that's attached to a brick wall, it's going to break. All this happens before the ball's momentum can be overcome to affect the top string.
 
please explain with momentum or ... formula(mathematical)
 
  • #10
The length and modulus of the strings (identical material, I assume) will affect the result, as well as the 'speed' and force applied. A helpful model would be to treat the strings as springs and the Spring - mass - spring - support would have different natural modes of oscillation. I don't think the calculations would be that hard to do (you'd need a bit of motivation). First write an equation of motion and solve it for the conditions. In the end, it's coupled oscillators. For a slowly applied force, the result will always be that the top string will break, of course.
 
  • #11
can you tell me a book help me?
 
  • #12
Better still watch the movie..

 
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