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Tornadoes form in the middle of thunderstorms when strong rising winds begin to spin. The spinning gets faster and starts moving downward like a funnel. When the funnel touches ground, it becomes a tornado with strong winds that can destroy almost anything in its path.

Topics and Connections:

• Tornadoes

Materials:

• vacuum cleaner with hose
• fan
• 5-pound block of dry ice [available from many ice suppliers (check your yellow pages).]

Directions:

Teacher:

• Discuss how these are similar to or different from real tornadoes. Have students investigate whether these tornadoes can lift anything into the air.

Students:

• Set the dry ice on the floor, with the fan about 15-20 feet away pointed towards it.
• Turn on the fan and wait a minute for the air to settle into a steady flow. The air will be moving more slowly at floor level, and more quickly a few inches above the floor. This difference in speed is an example of wind shear (see also the 'Watch the Wind' activity), and it can lead to tiny spirals in the dry ice fog.
• Set up the vacuum cleaner hose so it hangs about 6 inches above the block of dry ice and turn it on. Tornadoes will form between the dry ice and the hose. They last only a few seconds each, but new ones keep forming.

Follow Up:

• A much simpler, but less realistic, tornado can be made with two one-liter soda bottles and a 'tornadotube' that connects them. You can purchase such a tube in many large toy stores, science museum stores, or science supply catalogs.
• This is a water tornado, where a spinning whirlpool of water drains from one bottle into the other. Gravity keeps this 'tornado' going,and the tapering neck of the bottle forces the water to keep spinning faster. In a real tornado, air is moving upwards, against gravity, and the spinning motion comes from strong winds inside a thunderstorm.

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