A simple procedure can be followed to measure the coefficient of friction using the technique discussed in Example 5.11. Lay your book down on a table and place a coin on the cover far from the spine. Slowly open the book cover so that it forms an inclined plane down which the coin will slide. Watch carefully and stop opening the cover at the instant the coin begins to slide. (a) Measure this critical angle that the book cover makes with the horizontal with a protrac- tor. From this angle, determine the coefficient of static friction between the coin and the cover. (b) Place a loop of tape between two coins and repeat the procedure above for the two-coin stack. How does the coefficient of static friction for the stack compare to that for the single coin?