Fill one bottle 3/4 full with water.  Put empty second bottle on top of the first bottle so that the mouths are together.  Connect bottles with masking tape.

Vigorously churn bottom bottle as you turn both bottles over and place on a table.  Water forms a tornado funnel as it flows into the bottom bottle.

Fill one bottle with cold tap water and the other with hot tap water.  Drop different colored food coloring into each bottle.  Place a playing card or piece of cardboard on the opening of cold water bottle. Hold card tight against bottle as you turn the bottle over and place on the mouth of the hot water bottle.  Carefully remove card so that water from both bottles can mix.  What will happen and why?

Answer: Since heat rises, the hot water will flow up into top bottle as the cold water flows into bottom bottle.  The food coloring helps you see the movement of the water.

Tip: Its best to do this over the sink!

Pour about 3 inches of water into the jar.  Add 1/3 cup of vegetable oil and one drop of food coloring, then mix.   After the liquid settles, shake salt into the jar and count to 10.  Add more salt to continue the action.

What is happening?  
The oil floats on top of the water.  This is because oil is lighter, or less dense, than water.

Salt is heavier than water, so it sinks to the bottom.  As it falls, it grabs some oil and carries it to the bottom of the jar.  As the salt dissolves, the oil is released to return to the top.