Coefficients of static friction

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Discussion Overview

The discussion revolves around the coefficients of static friction for various combinations of human skin with different materials, specifically steel, aluminum, and wood. Participants explore the availability of these coefficients, methods for determining them, and the variability based on conditions such as skin type and moisture levels.

Discussion Character

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

Main Points Raised

  • Some participants inquire about the coefficients of static friction for human skin against steel, aluminum, and wood, seeking reliable sources for this information.
  • One participant notes that the coefficients can vary significantly depending on the condition of the skin, such as whether it is sweaty or calloused.
  • Another participant suggests that testing the friction coefficients directly may yield more accurate results than relying on potentially obscure data found online.
  • A participant mentions finding values for steel and aluminum around 0.2 and a value for wood around 0.91, but expresses uncertainty about their accuracy.
  • One suggestion for determining the coefficient involves a practical experiment using the skin on the forearm and measuring the angle at which a material begins to slide.
  • There is a discussion about the reproducibility of friction measurements, with some participants agreeing that conditions such as dryness or moisture can affect the results.

Areas of Agreement / Disagreement

Participants generally agree that the coefficients of static friction for skin against various materials can vary based on several factors, including skin condition and environmental conditions. However, there is no consensus on specific values or reliable sources for these coefficients.

Contextual Notes

Participants highlight the limitations of existing data, noting that coefficients may depend on specific conditions and that standardized testing methods may not be readily available for human skin.

cdorman
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Can anyone tell me the coefficients of static friction for these material combinations? Or does anyone know where I might be able to find them.
human skin - steel
human skin - aluminum
human skin - wood

Thanks
 
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cdorman said:
Can anyone tell me the coefficients of static friction for these material combinations? Or does anyone know where I might be able to find them.
human skin - steel
human skin - aluminum
human skin - wood

Thanks
It really depends to a great extent on which skin you're talking about and its condition, i.e., sweaty, calloused, etc.
The most readily available information will be for the bottom of feet and you might Google slip and fall and maybe add OSHA. I believe a lot of the data is for a standardized piece of pigskin, but you should get the idea.
 
Those are really obscure you don't have the sample of skin to actually test for the values? If but some random chance you can test it I would, the values would probably be hard to find on the internet...
 
yeah, they're kinda strange. I found the values for steel and aluminum which are bout around .2 and my teacher just sent a message saying that the value for wood is around .91 Hopefully they're right
 
cdorman said:
yeah, they're kinda strange. I found the values for steel and aluminum which are bout around .2 and my teacher just sent a message saying that the value for wood is around .91 Hopefully they're right

So, there's an easy way to actually determine this. Use the skin on the inside of your forearm. Find samples of wood, aluminum, and steel (you can use aluminum and steel jar lids with some weight added, or a heavy steel washer, or a weight with smooth aluminum foil wrapped around it). Place your arm flat on a table with the sample just above your wrist. Slowly raise your arm till the sample begins to move. Stop. Have a friend measure the angle of your arm wrt the table. The tan of that angle is the coefficient of static friction for that sample.
 
The friction coefficient is measured when the two surfaces are dry. So I do not think one can find reproducible values.
 
You're quite right that skin friction will be hard to reproduce. However, coefficient of friction is measured under many conditions - dry, wet, oiled, or with rosin (in the case of skin); you just need to say which way you've done it.
 

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