The Case of the Barfy Birthday (9 page)

The Scene:
You and your friend have built a magnificent tree house. The biggest one in the neighborhood. The highest one for miles around. The most comfy.

The Problem:
Now that you’re snug in your tree house, you and your friend realize you’re both very, very hungry.

You scramble down the ladder, shimmy down the wood blocks hammered into the tree trunk, and finally slide down the dangling rope until you reach the ground. Ahh, you think,
food
. And you load up for the trip back. (You know—cookies, cheese, sandwiches, pop, chips, etc.)

But at the base of the tree, you stop short. Uh-oh. A terrible question comes to mind. How do you get food to your tree house when you have to climb using both your hands? You know you can’t use a backpack to carry all your food, because you will then be too heavy to pull yourself up the rope. After all, remember, you’re
very, very
hungry and feeling a little weak. (Besides, what about that TV set that’s next on your list of tree house musts?)

Stumped? Try the following activity for a clue on how to make the work simple.

MATERIALS

• tape

• paper cup

• paper clip

• handful of small rocks

• string

• scissors

• 2 pulleys (available in hardware stores)

PROCEDURE

1. Cut a short piece of string and tape it securely to the top of the paper cup. This is your handle.

2. Put a handful of rocks into the cup.

3. Using another short piece of string, tie one of the pulleys to the back of a chair so that it hangs freely. This is pulley
A
.

4. Cut a piece of string three times as long as the height of the chair. For example, if the height of the chair is 4 feet, cut a piece of string 12 feet long [3 x 4 = 12].

5. Tie one end of the piece of string to the back of the chair. Thread the string through the second pulley (pulley
B
) and then through pulley
A
.

6. Secure the other end of the string by tying it to another piece of furniture so that your system remains tight and does not collapse.

7. Using the paper clip as a hook, attach the cup full of rocks to pulley
B
.

8. Untie the end of the string from the piece of furniture (see step #6). Pull string down to lift cup.

9. Up, down. Up, down. Snack time!

How Does This Work?

Pulley A changes the direction of the force. Instead of having to lift the cup up, you can now relax on the couch and pull the string down, with the same effect.

Using two or more pulleys divides the load. In this setup, if your rock-filled cup weighs 1 pound, pulley B reduces the weight (or force) you must pull by one-half. Now, instead of pulling 1 pound of rocks, you are pulling ½ pound. In return, you must pull twice the length of string. As a test, try the same setup
without
pulley B. Feel and see the difference?

“DO YOU SUPPOSE FRISCO, BALONEY, AND SHADY JIM ARE ALL IN IT TOGETHER?”
asked Drake, quite horrified by the thought.

June gasped. “But that would be cheating!”

“Cheating indeed, Ms. Jewell,” agreed Nell. “But it’s all we’ve got to go on right now.”

“Great Scott!” cried Drake. “Don’t look now. To your left. By the corn dogs. Under the licorice ropes. James Frisco! The very man!”

Drake and Nell sprang into action. They whipped out their magnifying glasses. They whipped out their periscopes. Their binoculars. Their insect repellant (it was a rather buggy day). They began surveillance, determined to expose Frisco, the
bad
mad scientist, at his game.