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Twister: What is the Shape of a Tornado?

based on 18 ratings
Author: Janice VanCleave

Problem

What is the shape of a tornado?

Materials

  • Two 2-liter clear plastic soda bottles
  • Tap water
  • Paper towel
  • Flat, metal washer with the same circumference as the mouth of the bottles
  • Duct tape
  • Adult helper

Procedure

  1. Ask your adult helper to remove the plastic rings left on the necks of the bottles when the lids are removed.
  2. Fill one bottle half full with water.
  3. Dry the mouth of the bottle with the paper towel and place the washer over the mouth of this bottle.
  4. Place the second bottle upside down on top of the washer.
  5. Secure the bottles together with tape.
  6. Turn the bottles upside down so that the bottle with the water is on top. Stand the bottles on a table.
  7. Place one hand around the lower bottle and the other hand on top of the upper bottle.
  8. Support the lower bottle while quickly moving the top of the upper bottle in a small counterclockwise circle.
  9. Stand the bottles upright, with the empty bottle remaining on the bottom.

Twister

Results

The water inside the upper bottle swirls in a counterclockwise direction, forming a funnel shape as it pours into the lower bottle.

Why?

The funnel formed by the swirling water is called a vortex (a whirling mass of air or water). The vortex formed in the water is the same shape as the vortex formed by a tornado (a violently rotating funnel cloud that touches the ground). A tornado looks like a swirling funnel hanging down from a dark thundercloud. The swirling air that forms the funnel of a tornado appears to begin at the bottom of a dark, puffy, cumulonimbus cloud and moves down to the ground. Sometimes a funnel cloud simply dangles in the air and then seems to disappear or be drawn back into the cloud. The funnel can consist of winds spinning at speeds of more than 400 miles (640 km) per hour. The length of the funnel extending from the sky varies, but it may be 2,000 feet (615 m) or more. The diameter of the funnel's destructive tip varies from a few yards (meters) to a thousand or more yards (meters), with an average diameter of about 400 yards (400 m).

Condensed water vapor inside the swirling funnel gives tornadoes their gray color. When a funnel cloud nears and/or touches the ground, it acts like a giant vacuum cleaner. The condensed water vapor plus dust, soil, and debris it sucks up makes it appear blackish.

Let's Explore

  1. Can the water swirl in the opposite direction? Repeat the experiment, rotating the bottle in a clockwise direction. Some scientists believe that tornadoes are set in motion by masses of air whose movements depend on the rotation of the earth. If this is true, all northern hemisphere tornadoes should spin in a counterclockwise direction and southern hemisphere tornadoes should spin clockwise. While that is usually the case, clockwise tornadoes have been seen in the northern hemisphere. Science Fair Hint: What do meteorologists think about the direction of the spin of tornadoes? Take a survey by asking for the opinions of several meteorologists, such as those reporting the weather for a local television station or for the national weather forecasting stations on the radio. Call or write letters to get the information.
  2. How does the energy applied to the bottles affect the results? Repeat the original experiment twice, first moving the bottle slowly and then moving it quickly. Compare the sizes of the funnels created in this experiment with the one produced in the original experiment. Science Fair Hint: Display drawings of the results and compare them to information about the production of different sizes of tornadoes.

Twister

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