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Content: Sometimes you can observe one thing to learn about something else you cannot directly observe. Scientists call this indirect observation. For example, although water molecules themselves are too small to observe, you can observe the way food coloring moves in water to try to learn more about the movement of water molecules.
Materials:
2 clear plastic cups (per student or group)
hot tap water
cold water
food coloring (blue and yellow or red and blue or red and yellow)
white sheet of paper
Procedure:
Fill one cup about 3/4 full with cold water and the other cup about 3/4 full of hot water. Allow the cups to stand for about 1 minute so the water is very still.
Gently, place 1 drop of blue and 1 drop of yellow food coloring in the very center of the surface of each cup.
Hold a white piece of paper behind the cups so that you can observe the food coloring very clearly.
Describe what the food coloring looks like in each cup.
Based on your observation of the food coloring, what do you think is the difference between the way water molecules act in cold water compared with hot water?