Teaching Physics with the Physics Suite

Edward F. Redish

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The book and the wall

You are holding your physics book against the wall by pressing on it as shown in the figure at the right.

(a) You are pressing hard enough so that the book doesn’t move. Draw a free-body diagram for the book, being sure to identify all the forces that might be acting on the book. For each force the kind of force, what object is causing it, and what object is feeling it.

(b) What relations are there among the forces in your diagram? That is, which forces or sums of forces have to be equal? How do you know?

(c) You begin to get tired and the book begins to slide down. The book begins to slide down, and you respond so it slides down at a constant velocity. How do each of the forces you have identified change from their magnitudes in part (a)? Explain how you know.

Page last modified September 21, 2011: D39