Make a “Tornado in a Bottle.”
Fill one of the soda bottles about two-thirds full of water. Add a little food coloring or paper bits to the water. Screw the bottles onto both ends of the plastic connector. (CAUTION: Do not screw the connector on too tightly!) Or you can tape the bottles together with the washer between them.
Place the bottles on a table with the filled bottle on top. Watch the water slowly drip down into the lower bottle as air bubbles up into the top. Rapidly rotate the bottles in a circle a few times and stop. Observe the formation of a funnel-shaped vortex as the bottle drains. Also, notice the flow of the water as it empties into the lower bottle.
You can make the vortex with a single bottle by twirling the bottle and holding it over a water basin or the ground to drain, but you lose the water and have to refill the bottle each time you use it.
What happens when you pull the drain after taking a bath? Which direction does the water flow down the drain? What other natural vortices have you seen?
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