Calculating Coefficient of Friction for Sandpaper

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Discussion Overview

The discussion revolves around calculating the coefficient of friction for sandpaper in the context of testing the mechanical resistance of a bioplastic. Participants explore theoretical aspects of friction, its dependence on various factors, and practical considerations for measurement.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the method to calculate the coefficient of friction, specifically in relation to the mechanical testing of bioplastics.
  • Another participant suggests that the coefficient of friction can be determined by the tangent of the angle at which slippage begins.
  • A clarification is sought regarding the angle's orientation and the role of mass in determining the coefficient of friction.
  • It is proposed that friction is directly proportional to mass and that the coefficient of friction is often considered independent of contact area, although this may not hold true in all scenarios.
  • Concerns are raised about the oversimplification of friction laws, particularly in relation to abrasive materials, suggesting that actual measurements may be necessary to understand the behavior of the specific sandpaper being used.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between mass, contact area, and the coefficient of friction, indicating that there is no consensus on these aspects. The discussion remains unresolved regarding the exact nature of these relationships in practical applications.

Contextual Notes

Participants note that the assumptions underlying the laws of friction may not apply uniformly to all materials, particularly in the case of sandpaper, and emphasize the need for empirical measurements to validate theoretical claims.

hello1910
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Hello Fellow Forum,

How would you calculate the coefficient of friction for sandpaper? I'm testing mechanical resistance of a bioplastic, and I'm going to attach the bioplastic to different weights, and then rub sandpaper over the bioplastics. The one that breaks will be used to find mechanical resistance. I know F=un- and n= the weight of the object the plastic was attached to, but how do you calculate u?
Thanks
hello1910
 
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The coefficient of friction is equal to the tangent of the angle where slippage is initiated.
 
Thanks for the quick reply! Just to clarify, the angle is between the bioplastic and the weight, right? And also, you're saying that mass has no effect on the coefficient of friction?
 
The friction is in direct proportion to the mass. Friction is often considered independent of contact area. If we want to change the friction we change the materials.

Does that mean a one tonne object on a 1 square mm leg is the same friction as on 100 square meter support. Not likely for normal materials.

Is it the same once movement starts? No. Is it constant at different velocities? It depends.

You are interested in the static coefficient of friction and the kinetic coefficient of friction.
http://en.wikipedia.org/wiki/Friction

The science is tribology http://en.wikipedia.org/wiki/Tribology
 
Last edited:
The 'laws' of friction assume that there is elastic deformation of the surfaces to that the actual contact area (on a microscopic level) depends upon the normal load and not on the available area for contact between the surfaces - so that the friction force increases proportionally with the normal load - giving a 'constant' coefficient. This is an oversimplification for many situations. An abrasive paper is not likely to be that ideal - you could imagine the limiting case of barely visible grooves with vertical sides on both faces that could 'lock' together. The 'friction' force could be the same for all normal loads once the surfaces were in contact.
You would need to do some actual measurements with the abrasive that you are planning to use and find the range over which you have linearity.
 

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