Smoke Rings

Purpose - To observe the downward flow ofcold colored water through warmer clear water.

Materials - 1 ice cube

smallbaby-food jar

1 large-mouthed, clear, glass, quart (liter) jar warm and cold tap water eyedropper red foodcoloring

6-inch (15-cm) square aluminum foil

rubberband

pencil

Procedure

■ Place the ice cube in thebaby-food jar. Fill the jar with cold water.

■ Fill the quart jar to within aninch of the top with warm tap water.

■ Remove the ice cube from thebaby-food jar. Add and stir in 6 to 7 drops of food coloring.

■ Cover the mouth of the baby-foodjar with aluminum foil. Use the rubber band to secure the foil around the mouthof the jar.

■ Use the point of a pencil to makea small hole in the aluminum foil.

■ Quickly turn the baby-food jar upside down andhold it so that the hole is just beneath the surface of the warm water.

■ Slowly and gently tap the bottom of thebaby-food jar with your finger.

Results The cold colored water flows downward. Thetapping causes the colored water to come out in spurts, producing smoke-likerings of color in the warm clear water.

Why? The molecules of water, like all matter, arespaced closer together when cold and farther apart when heated. Thus, each dropof cold water has more water molecules and is heavier than a drop of warmerwater. Since the cold water is heavier, it sinks down through the warmer water. The food coloring has little effect on the weightof the coldwater.

Smoke Rings