Flag Raiser: What is a Fixed Pulley, and How Does it Make Your Work Easier?

Problem

What is a fixed pulley, and how does it make your work easier?

Materials

• pencil (must be small enough to slide through the hole in the thread spool)
• large, empty thread spool
• scissors
• ruler
• string
• sheet of typing paper
• 2 sheets of construction paper (1 blue, 1 red)
• glue
• masking tape

Procedure

1. Place the pencil through the hole in the thread spool. The spool must turn easily on the pencil.
2. Cut a 6-foot (2-m) piece of string, and tie the ends of the string together.
3. Use the following steps and diagram to make a small American flag.
   • Cut the sheet of typing paper in half. Hold one of the pieces aside, and cut some stars out of the other piece.
   • Measure and cut a 3-inch (7.5-cm) square from the sheet of blue construction paper. Glue this square in the upper left-hand comer of the white paper, and glue the stars to the blue paper.

   

   • Cut six red strips of paper about 1/2 inch (1.3 cm) wide, and glue them to the paper, as in the diagram.
4. Tape the side of the flag with the stars to the string.
5. Place the loop of string over the spool, with the flag hanging at the bottom of the loop.



6. Ask a helper to hold the ends of the pencil, one in each hand at arm's length over his or her head.
7. Pull down on the string opposite the flag.
8. Observe the distance the string is pulled down and the distance and direction the flag moves.

Results

The length of string pulled down over the spool equals the distance the flag moves upward.

Why?

A pulley is a simple machine that consists of a wheel, usually grooved, that holds a cord. A fixed pulley stays in place; the pulley turns as the cord moves over the wheel, and a load is raised as the cord is pulled. The spool is a fixed pulley that allows you to pull down on the string and raise the flag upward. Placing a fixed pulley at the top of a tall flagpole makes the job of raising a flag easier than if you had to carry the flag up the pole. A fixed pulley makes work easier by changing the direction of the effort force.

Let's Explore

Would the size of the spool affect the results? Repeat the experiment twice, first using a smaller spool, and then using a larger spool. If the smaller spool does not easily turn around on the pencil, replace the pencil with a rod of smaller diameter.

Show Time!

1. A pulley that raises bricks to the top of a building is an example of a fixed pulley. Find out more about fixed pulleys, and display pictures of their uses.



2. Build a moveable clothes line using thread spools and large paper clips. You can do this directly on a project display board. Bend each paper clip as indicated in the diagram. Slip the spool onto the wire, and bend the end of the wire up so the spool will not slip off. Position the spools across from each other on the display, and tape the wire to the display so that the spools stand upright. Attach a string around the spools, and tie the string. Use small clothespins or bobby pins to attach doll clothes to the clothesline. Pull the string to demonstrate the use of the fixed pulleys to move the clothes from one side of the display to the other.

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Janice VanCleave's Machines
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