Windy: How Can the Speed of Wind be Measured?

Problem

How Can the Speed of Wind be Measured?

Materials

• Drawing compass
• Poster board square, 6 × 6 inches (15 cm × 15 cm)
• Scissors
• Ruler
• Marking pen
• Transparent tape
• 12-inch (30cm) piece of thread
• Ping-pong ball

Procedure

1. Use the compass to draw a curved line connecting two diagonal corners of the piece of poster board as shown in the diagram.
2. Cut along the curved line and keep the cone-shaped piece of paper. Discard the rest.
3. Lay the paper on a table with one straight edge at the top and the other straight edge to the right.
4. pare a scale on the curved edge of the paper by using the ruler and pen to make nine evenly spaced sections along the curved edge. Number them, starting with zero, as shown in the diagram.
5. Draw an arrow along the top edge pointing toward the corner of the paper.
6. Turn the ruler over and tape the paper to the top edge of the ruler as shown.
7. Tape one end of the thread to the Ping-Pong ball.
8. Tape the other end of the thread near the corner of the paper. The thread should hang so that it crosses the zero mark on the paper.
9. Stand outside in a windy area. Hold the ruler and point the arrow in the direction from which the wind is blowing.
10. Observe where the string crosses the paper scale.

Results

In a gentle breeze, the string moves slightly from its vertical position. A faster breeze causes the string to move farther up the scale.

Why?

The instrument you built is called an anemometer. An anemometer is used to measure how fast the wind blows. Moving air hits the Ping-Pong ball and causes it to move. The speed of the wind hitting the ball is indicated by the scale number to which the ball moves, as determined by the position of the string across the paper scale. The higher the number, the faster the wind is blowing.

Let's Explore

Use the anemometer you just made to measure the wind speed each day for a week or more. Record your readings in a data chart. Science Fair Hint: Use the information from the data chart to construct a graph similar to the graph shown here. Display the chart, graph, and anemometer as part of a project display.

Show Time!

1. Construct another type of anemometer called a Robinson anemometer by crossing two drinking straws and taping them together in the center where they cross. Use a pencil to punch a hole in the side of a 3-ounce (90-ml) paper cup near its rim. Do the same to three other cups that size. Place a cup on the end of each straw and secure with tape. All of the cups must face in the same direction. Ask an adult to stick a straight pin through the center of the straws and into the eraser of a pencil. Move the straws back and forth to enlarge the hole made by the pin so that the straws rotate easily around the pin. Hold the pencil upright and position the cups about 12 inches (30 cm) from your face. Blow toward the open end of the cups to make sure the cups will spin around in a breeze. Use the cups to make comparisons of wind speeds on different days. The speed of the wind hitting the cups is determined by the number of turns per minute made by the cups. The faster the wind, the more turns per minute. Use this anemo eter to determine wind speed (number of turns per minute) over several days. Compare your results with predicted wind speed from daily weather reports in the newspaper and/ or local television. Display the anemometer and the collected results
2. You can figure out the wind's direction simply by observing which way tree limbs, shrubs, or grass are blowing and then using a compass to determine what direction that is.
3. A weather vane (instrument that shows wind direction) can be constructed by marking the directions, N, NE, E, SE, S, SW, W, and NW along the rim of a paper plate. Place the plate on the ground in an unobstructed area. Attach a 4-inch (10-cm) piece of string to the top of a pencil eraser with a piece of tape. Insert the point of the pencil through the center of the paper plate and about 1 inch (2.5 cm) into the ground. Use a compass to determine which way is north, and rotate the paper plate until the N marked on the plate points north. The string will blow in the same direction as the wind. Photographs of the weather vane can be displayed.

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Janice VanCleave's Weather
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