If i have two coefficients of kinetic friction. One is a book pressing against a shirt at ceofficient .32 and the other is the shirts friction against the book at a coefficient of .16.

I am real sorry for asking this but my book does not explain to me how to deal with problems that involve more that one coefficient. I was wondering how I am suposed to calculate the force with two different coefficients. I thought about adding them, simply because 2 rough edges would be rougher, but something tells me its wrong.

I'm not sure. The coefficient of friction is always given for two surfaces in contact, not for one surface. Isn't it? Maybe you read it wrong?

Web definitions for Coefficient of Friction
The coefficient of friction (also called COF, or friction) is a measurement of the force it takes to slide an object across another surface divided by the object's weight. In bowling, the coefficient of friction refers to how well the bowling ball grabs the lane surface. If lane oil is present the ball slides on the lane surface very easily and there is a low COF. If there is no oil on the lane, the ball does not slide as easily and the coefficient of friction is high. ...
www.eleventhframe.com/bote.html

that is really retarded.

i'd guess that if the title for the coefficients is stated as "book pressing against the shirt" and "shirt pressing against the book" then maybe you simply need to see which one is pressing against which and use the corresponding coefficient.

if it is a matter of life and death, you should paste the entire text exactly here.
if not, dont worry about it. this is in no way the standard form of friction problems and you dont really need to care about it confusing you as it will confuse any physics teacher on the planet.

The coefficient of friction, as Rosnet says, is characteristic of the contact between 2 surfaces. Therefore, it is impossible to have 2 different coefficients in the sense of the first post.

The question goes something like this.

Bob has a physics book between his arm and ribs. The coefficient of friction of his shirt is .16 and the coefficient of friction of the book is .32. If the book has a mass of 10.2 kg then how much horizontal force does Bob need to apply in oder to hold the book.

Now I am assuming the horizontal force = (the weight of the book)(ceofficient of friction). Right? How do I apply two different ceofficients on the same problems.

I apologize if its a stupid question and the answer ends up being right in front of me. I just don't see it. One of the things I hate the most in life is not being able to solve a problem.

Hi JetPilot,
It's not your fault - the author of the text has been sloppy when wording the question.
The coefficients in the question aren't stated clearly, but I think that it means:
1) The coefficient of friction between the book and Bob's shirt is 0.32
2) The coefficient of friction between Bob's shirt and Bob's skin is 0.16

Since you aren't given the coefficient of friction between the book and Bob's skin, I think you'll have to assume that Bob's wearing a long-sleeved shirt.

Nope. The friction between his body and his shirt doesn't matter. The shirt doesn't stay on because of friction exactly (well at the deeper level, that's involved but you know...).
It must be that the coefficient of friciton between the book and the shirt is .16, and that between the book and the hand is .32. And the values make sense too...

Yep, that makes more sense.

So what it means, JetPilot, is that you have a 0.16 coefficient of friction on one side of the book, and a 0.32 coefficient on the other.

You still need to think about what to do with that information - it's not immediately obvious.

Thanks for the help guys.