Materials Needed:
- 1 large textbook
- 12 coins (similar size)
Procedure: (see Figure 11)
- Put the heavy hardcover book flat on the table.
- Rotate it slowly back and forth and get a feel
for how hard it is to turn.
- Put a stack of 3 coins on the table and balance
the book on them.
- Rotate it slowly back and forth again and note
how hard it is to turn. (do not let the
edges of the book touch the table)
- Put a stack of 3 coins under each corner of the
book.
- Rotate it slowly back and forth again and note
how hard it is to turn.
- Repeat the last 2 steps each time moving the
coin stacks closer to the center.
- Is the flat book harder to turn because of more
surface area in contact with the table?
Figure 11: Friction investigation setup
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Observations:
Where things are rubbing together makes a difference. Much
like a lever, the farther from the center (pivot) a force is,
the more effect it has. It is easier to stop spinning objects
by grabbing the outside edge than a point near the middle.
Therefore, a friction force far from the center slows a spinning
object (such as a wheel) more quickly than the same force
close to the center.
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