College Physics
1st Edition
ISBN: 9781938168000
Author: Paul Peter Urone, Roger Hinrichs
Publisher: OpenStax College
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Chapter 5, Problem 4CQ
When you push a piece of chalk across a chalkboard, it sometimes screeches because it rapidly alternates between slipping and sticking to the board. Describe this process in more detail, in particular explaining how it is related to the fact that kinetic friction is less than static friction. (The same slip-grab process occurs when tires screech on pavement.)
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A ski that is placed on snow will stick to the snow. However, when the ski is moved along the snow, the rubbing warms and partially melts the snow, reducing the coefficient of friction and promoting sliding. Waxing the ski makes it water repellent and reduces friction with the resulting layer of water. A magazine reports that a new type of plastic ski is especially water repellent and that, on a gentle 230 m slope in the Alps, a skier reduced his top-to-bottom time from 69 s with standard skis to 42 s with the new skis.
Old skis acceleration = 0.097 m/s2
New skis acceleration = 0.26 m/s2
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A physics textbook lies flat on a horizontal table top. The book's front cover is facing up. If you slide the book very, very slowly toward the edge of the table (by pushing it horizontally, not by pulling it), it will eventually fall off and land on the floor. We did this experiment in one of our Class Meetings and the result was that the book most likely will end up on the floor with its front cover facing down.
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Chapter 5 Solutions
College Physics
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