# Understanding μk

 P: 2 I'm currently a first year physics student and missed some nets and concepts and need help before exams. It would be a HUGE help if someone could explain it to me and how to use it to find things like Fn and a→ when mass and μk is given. Please i really could use this info and thanks.
 Homework Sci Advisor HW Helper Thanks P: 13,070 Welcome to PF; By ##\mu_k## do you mean the coefficient of kinetic friction? It's used the same way as any coefficient of friction. You use friction as an additional force in the free-body diagram. People tend to trip up on the direction (it changes if the velocity changes direction) and on the transition between kinetic and static cases. See: http://hyperphysics.phy-astr.gsu.edu/hbase/frict.html Hyperphysics appears to repeat an "obsolete idea" about friction re surface roughness. See: http://amasci.com/miscon/miscon4.html#fric ... does not affect the calculation though.
 P: 2 yeah i was talking about it as as a coefficient of friction kinetic friction and thanks for the help!
 Mentor P: 41,317 Understanding μk I'm impressed you were able to decode that, Simon! I didn't have a clue what the OP was asking...
 Homework Sci Advisor HW Helper Thanks P: 13,070 @T_razz: no worries, do some examples and let me know if you get stuck. @berkeman: experience :D I need to edit my original reply slightly though: the coefficient is not the force. I'm sure nobody got confused...
 Sci Advisor Thanks PF Gold P: 12,261 Psychic?
 Homework Sci Advisor HW Helper Thanks P: 13,070 I dunno - lets see... ummmm... I'm picking up an impression of a square or rectangle of light in front of you... also a general blockyness like an ordered cubism regularly under your hands. There's another in the background - it's fuzzy - associated with the letter D or C. Does this make any sense to you?

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