Does acceleration cause a string to stretch?

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Discussion Overview

The discussion revolves around the effects of acceleration on the stretching of a string in the context of a pendulum system. Participants explore how the tension in the string changes when the pendulum bob is at rest versus when it is in motion, particularly at the bottom of its swing.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions whether the wire supporting a pendulum bob stretches more when the bob is in motion compared to when it is at rest.
  • Another participant agrees, using the analogy of a swing where the rope slackens at higher points and becomes taut at midswing.
  • A participant inquires about the forces acting on the bob at the bottom of the swing, specifically asking about the change in tension compared to the top of the swing.
  • One participant suggests that the tension in the string at the bottom of the swing should be the same as if it were at rest, implying that it would be less when the bob is higher.
  • Another participant introduces the concept of centripetal force, noting that the bob's high speed at midswing creates a force that the string must counteract.
  • A later reply proposes a practical experiment to demonstrate that the elastic stretches more when the weight is swinging compared to when it is hanging vertically.

Areas of Agreement / Disagreement

Participants express differing views on whether the tension in the string at the bottom of the swing is the same as when at rest, indicating a lack of consensus on the effects of acceleration on string stretching.

Contextual Notes

Participants have not fully resolved the assumptions regarding the forces acting on the pendulum bob and how these relate to the tension in the string at different points in the swing.

Who May Find This Useful

Readers interested in mechanics, pendulum dynamics, and the effects of acceleration on tension in strings may find this discussion relevant.

rezihk
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if you have a pendulum with a 10kg bob at rest, it causes a stretch in the wire supporting it, but if that same bob were to be let go at a certain angle from the vertical, would would the wire stretch more as the bob reaches the bottom of its swing where the speed is the greatest?

in order words

stretch of wire with acceleration > stretch of wire when at rest?
 
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i would say so. Consider someone on a swing as they go higher and higher the rope actually slackens and then at midswing its taunt again.
 
Last edited:
so what other forces would be acting on the bob at the bottom of the swing apart from mg?

by what factor would the tension change at the bottom as compared to the top of the swing?
 
shouldn't the tension in the string at the bottom of the swing be the same as if it were at rest, and then it be less when it higher?
 
since the bob is moving very fast at midswing it wants to go straight ahead but the string is preventing that so there's a component of centripetal force right.
 
Do an experiment. Make a pendulum by tying a weight to the end of a piece of elastic. Hang the pendulum above a table, so the weight is just touching the table. Then start it swinging from a horizontal position, and be careful that you are not stretching the elastic when you let the weight go.

The weight will hit the table, showing that the elastic has stretched more than when it was hanging vertically but not swinging.
 

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