# 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 as shown in Figure P4.82. The angle of the incline, θ 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 μ s n for angles less than θ C ? Explain. What can you definitely say about the magnitude of the friction force for any angle θ ≤ θ c ? (c) Show that the coefficient of static friction is given by μ s = tan θ c . (d) Once the coin starts to slide down the incline, the angle can be adjusted to a new value θ c ’ ≤ θ c such that the coin moves down the incline with constant speed. How does observation enable you to obtain the coefficient of kinetic friction? Figure P4.82 BuyFind

### College Physics

10th Edition
Raymond A. Serway + 1 other
Publisher: Cengage Learning
ISBN: 9781285737027 BuyFind

### College Physics

10th Edition
Raymond A. Serway + 1 other
Publisher: Cengage Learning
ISBN: 9781285737027

#### Solutions

Chapter 4, Problem 70AP
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