# Coefficients of static friction

1. Dec 19, 2007

### cdorman

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

2. Dec 19, 2007

### TVP45

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.

3. Dec 19, 2007

### Feldoh

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...

4. Dec 19, 2007

### cdorman

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

5. Dec 20, 2007

### TVP45

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.

6. Dec 20, 2007

### pixel01

The friction coefficient is measured when the two surfaces are dry. So I do not think one can find reproducible values.

7. Dec 21, 2007

### TVP45

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.