Are Coefficients of Friction Independent of Weight?

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    Coefficients Friction
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Discussion Overview

The discussion centers on whether the coefficients of static friction (Ms) and kinetic friction (Mk) are independent of the weight being pulled. Participants explore this concept in the context of a lab experiment involving friction, with a focus on theoretical and practical implications.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant questions if coefficients of friction are independent of weight, referencing a lab experiment.
  • Another participant asserts that in examination questions, coefficients of friction are typically considered independent of weight, but notes that real-world applications may differ.
  • It is mentioned that coefficients of friction can vary based on surface conditions and that trials are the best method for determining them.
  • A participant suggests that reducing the weight from 1 kg to 0.5 kg while dragging a block would not change the coefficients of friction, arguing that friction is directly proportional to weight but remains constant in terms of the coefficients.
  • Another participant agrees with the idea that the coefficients should remain the same based on the reasoning provided.

Areas of Agreement / Disagreement

While some participants agree that coefficients of friction should remain the same regardless of weight, there is an acknowledgment of the complexity of real-world scenarios, suggesting that the discussion remains somewhat unresolved regarding practical applications.

Contextual Notes

Participants note that the coefficients of friction can be influenced by factors such as surface conditions and pressure, indicating that assumptions about independence from weight may not hold in all situations.

mybrohshi5
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Are coefficients of friction Ms and Mk independent of the weight being pulled?

We just had a lab on friction and i am just curious about this.

Thank you
 
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Hi mybrohshi5! :smile:

(have a mu: µ :wink:)

In examination questions, µs and µk are always independent of weight. :wink:

In reality, see this, from the PF Library on friction:

Tables of coefficients of friction:

Many tables can be found on a http://www.google.com/search?client...ficients+of+friction+table&ie=UTF-8&oe=UTF-8", which begins
"Extreme care is needed in using friction coefficients, and additional independent references should be used. For any specific application the ideal method of determining the coefficient of friction is by trials. A short table is included above the main table to illustrate how the coefficient of friction is affected by surface films. When a metal surface is perfectly clean in a vacuum, the friction is much higher than the normal accepted value and seizure can easily occur."
For some materials, the coefficient can be greater than one, and for solids on rubber it can be as high as four.

Increasing pressure between dry surfaces may increase the coefficient, at first slightly, but eventually very quickly, leading to seizing. For this and other factors affecting coefficients of friction, see the top box in http://www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm"
 
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Thanks tiny-tim.

In my lab we used about a 1 kg weight on top of a wooden block and that was dragged across the table.

So say i reduced that weight down to 0.5 kg and dragged it again would the coefficients of friction be the same or different?

From what i got from the websites you posted i think the coefficients of friction will be independent of the weight therefore making them stay the same because...

...since relatively low pressures are being used then the friction would go down as the weight goes down and the friction would go up as the weight goes up (to an extent) so basically i am saying that the friction is directly proportional to the weight so µk and µs will stay the same making them independent of the weight being pulled...
 
Hi mybrohshi5! :smile:

Should be the same, for exactly the reasons you've given.

(But you should still try it! :wink:)
 
Thank you. That helped clear up a lot of things for me :)
 

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