Optimizing String Placement for Accurate Friction Experiments

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Discussion Overview

The discussion revolves around the significance of string placement in friction experiments, specifically the importance of keeping the string parallel to the horizontal plane. Participants explore the implications of string angles on the measurement of frictional forces and normal forces.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question why the string must be parallel to the ground in friction experiments.
  • One participant asserts that the scale reading reflects the force required to pull the object, suggesting that trigonometric calculations are unnecessary.
  • Another participant emphasizes that an angled string would alter the normal force acting on the weights, affecting the friction measurement.
  • Participants discuss the consequences of the string being angled up or down, noting that it would either reduce or increase the normal force, respectively.
  • One participant expresses confusion regarding the explanation of the string's significance and seeks clarification.
  • A later reply proposes considering an extreme case where the string forms a steep angle, prompting further inquiry into what the scale would measure in that scenario.

Areas of Agreement / Disagreement

Participants generally agree on the importance of the string's orientation in relation to the normal force, but there is uncertainty and confusion regarding the implications of different angles and the overall explanation of the setup.

Contextual Notes

Some participants express confusion about the relationship between string angle and normal force, indicating a potential lack of clarity in the explanation provided. The discussion does not resolve these uncertainties.

kiddiegrade
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Why does the string in an experiment setup fro friction experiment be parallel to the horizontal plane? What is its significance? (see picture attached)
 

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First, and most important, the reading on the scale will be the amount of force required to pull the doowhat on the left hand side. You won't need trig to figure out force components and whatnot.
 
But our teacher says that it is important that the string is parallel to the ground.. why?
 
kiddiegrade said:
But our teacher says that it is important that the string is parallel to the ground.. why?

Because the experiment is attempting to measure the frictional force that is produced by a particular normal force.

If the string were angled up slightly as it goes toward the scale then it would be pulling up on the weights. They would be pressing down with less than their full weight on the ground since they would be partially supported by the string. The normal force would be reduced.

If the string were angled down slightly as it goes toward the scale then it would be pulling down on the weights. They would be pressing down with more than their full weight on the ground. The normal force would be increased.
 
Because the experiment is attempting to measure the frictional force that is produced by a particular normal force.

If the string were angled up slightly as it goes toward the scale then it would be pulling up on the weights. They would be pressing down with less than their full weight on the ground since they would be partially supported by the string. The normal force would be reduced.

If the string were angled down slightly as it goes toward the scale then it would be pulling down on the weights. They would be pressing down with more than their full weight on the ground. The normal force would be increased.

I do not understand.. sorry.
 
kiddiegrade said:
I do not understand.. sorry.

Think about the extreme case. Suppose you allowed the string to form a very steep angle with the surface, say ninety degrees. Then what would the scale be measuring?
 

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