# Physics

Measuring coefficients of friction. A coin is placed near one edge of a book lying on a table, and that edge of the book is lifted until the coin just slips down the incline. The angle of the incline Theta C, called the critical angle, is measured. (a) Draw a free body diagram for the coin when it is on the verge of slipping and identify all forces acting on it. Your free-body diagram should include a force of static friction acting up the incline. (b) Is the magnitude of the friction force equal to mu s n for the angles less than Theta C? Explain. What can you definitely say about the magnitude of the friction force for any angle Theta smaller or equal Theta C? (c) Show that the coefficient of static friction is given by mu s = tan Theta C. (d) Once the coin starts to slide down the incline, the angle can be adjusted to a new value Theta' C smaller or equal Theta C such that the coins moves down the incline with constant speed. How does observation enable you to obtain the coefficient of kinetic friction?

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