Tornado Tube

Concepts – potential energy, kinetic energy, density, air pressure

Materials – two 1-liter bottles, water, tornado tube connector, optional: electrical tape

Procedure – fill one of the liter bottles ¾ the way up with cold water. Twist the tornado tube connector on to the top of the bottle. Take the other liter bottle that is filled only with air and twist it to the top of the tornado tube connector. You will end up with a linear bottle-with-water/tornado tube connector/bottle-with-air configuration. Turn the bottles over so the one with water is on top. Holding the top of the bottle begin swirling the bottle in a circular motion until you see a funnel forming in the water. Ask students what causes the formation of the funnel and why it continues to appear even after you stop moving the bottle in a circular motion. Additionally, have students relate what they observed in the bottles to occurrences in nature.

Explanation – A tornado tube works similar to the way a real tornado does. In a tornado tube the denser water is above the less dense air. In order for the air to rise and the water to fall they must change places, and when they do so they must past one another. Much like two people moving opposite ways through a doorway, they must move over so both can fit through the space. The circular motion of the water allows water to swirl around the outside of the bottle while the air travels up the center of the tube. Gravity forces the water down while the water forces the air up.

Another way to describe tornado tubes is in terms of energy. The water in the top bottle has gravitational potential energy because of its position above the bottom bottle. As the water falls this energy is changed into kinetic energy. When the water reaches the lower bottle it performs work on the air and gives it kinetic energy. The air subsequently moves up to the top bottle and as it does some of its kinetic energy is transferred into gravitational energy.

In nature the different types of vortexes include tornadoes, hurricanes, whirlpools and dust devils. In all cases less dense material wishes to rise while denser material wishes to fall. In a real tornado, a cold and a warm front meet. Layers of the cold, dense air wind up on top of the warm, wet, less dense air. The cold air wants to go down and the warm air wants to rise and the result is a vortex.

Extension – for some neat effects add a drop of dishwashing soap, food coloring, or glitter to the water in the tornado tube.

Figure 29: A tornado tube creates a vortex in the top bottle.

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