Turn the cups so that they face the same direction. Push the empty end of each straw into one of the side holes in the five-hole cup and out the one across from it.Repeat this with another single-hole cup and straw. Make sure the straw is horizontal and staple it to the side of the cup. Take a single-hole cup and push a straw through the hole until about one inch of the straw is inside the cup.Also punch one hole in the center of the bottom. For the fifth cup, punch four equally spaced holes in its sides, about one quarter an inch below the rim.Prepare four cups this way: Punch one hole in the side of each cup, about one half an inch below the rim.Five three-ounce paper cups (such as Dixie Cups).Consequently, faster wind will result in a higher rpm than will a slower air movement. How fast the cups revolve can be measured in revolutions per minute (rpm), or how many times one cup returns to the position where it started in one minute. When wind pushes the cups on the anemometer, they spin around the central axis. This movement of air from a higher pressure area to a relatively lower pressure area is what generates wind. In comparison, cold air is made of more tightly packed molecules, and so it is denser and has relatively higher pressure.īecause air pressures are inclined to balance out, when there is an area of relatively lower air pressure, the surrounding air in higher pressure areas moves in. This also means that the air has a lower overall pressure. Consequently, when air is heated, its molecules move faster and become spaced farther apart, which makes the air less dense (meaning that there are fewer molecules in a given volume). When molecules are heated, they move faster. How fast will your homemade anemometer whirl?Īir is made up of tiny molecules. The faster the wind, the faster the cups spin the axis. When wind pushes into the cups, they rotate the axis. Each cup is attached to the end of a horizontal arm, each of which is mounted on a central axis, like spokes on a wheel.
The speed of that wind can be measured using a tool called an anemometer.Īn anemometer looks like a weather vane, but instead of measuring which direction the wind is blowing with pointers, it has four cups so that it can more accurately measure wind speed. And just as air flows out of the high-pressure inside an inflated balloon if the opening is not tied, air in the atmosphere will move to a lower pressure area, creating wind. Air travels from areas of higher pressure to places where there is less pressure.
Have you ever wondered how wind is made? Wind is caused by a difference in air pressure.
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