Things You Will Need
- Two sharpened pencils
- Empty thread spool (larger size)
- Two small paper cups
- 20 pennies
- Masking tape
- Marking pen
- Single-hole puncher
- Stick the pointed end of a pencil snugly into each end of an empty thread spool. The pencils should not slide when in the holes.
- Cut two 18-inch pieces of string. Fold each piece into a loop. Tape one end of each loop near the edge of a table or counter so that most of the loop hangs freely off the edge.
- Place each pencil through one loop so that the pencils and spool are hanging level off the edge of the table or counter.
- Punch a hole near the rim of a small paper cup and a second hole on the opposite side. Do the same to a second paper cup.
- Cut a 24-inch piece of string and attach one end through the holes of a cup. Cut a second 24-inch piece of string and repeat for the second cup.
- Label the cups A and B.
- Tape the free end of cup A's string to one of the pencils. Turn the pencils away from you to wind all the string onto the pencil.
- Tape the free end of cup B's string to the center of the thread spool. Turn the pencils toward you to wind cup B's thread onto the spool. Cup B should be at the top position and Cup A should be at the bottom position.
- Place 10 pennies in cup A.
- Add pennies to cup B one at a time until it slowly moves downward. How many pennies are needed to make the cups move? Do the cups move at an equal distance?
What Should Have Happened
The cups do not move at an equal distance. Cup B moves a greater distance than cup A. The distance around the spool is more than the distance around the pencils. Therefore, with every turn, the cup attached to the spool moves farther than the cup attached to the pencil. This is a simple machine called a wheel and axle.
Webdate: June 11, 2002
Updated: July 2004
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