The figure shows pencils being used as rollers under a heavy book.  The book becomes easier to move because:
ARolling friction is less than sliding friction
BThe pencils make the book lighter
CThe pencils transfer the weight to the wall
DThe pencils eliminate friction completely
Answer & Solution
Correct answer: A. Rolling friction is less than sliding friction
When one body rolls over another (here, the book on the pencils), the resistance to motion is called rolling friction. Rolling friction is much smaller than sliding friction, so it is easier to push the book on rollers than to slide it directly across the table — which is the same principle that makes the wheel one of the most useful inventions.
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