For example, they might find out whether or not their telephones will work when their lines are stretched through a closed door, or when their fingers are pressed against the bottom of the cup. Before they try an experiment, you might want to have them write down the procedure and the expected results. After trying the experiment, they can record their results and try to explain why or why not their prediction came true. Bring students back to the original question. Ask them how they can use what they've learned with the paper cup telephone to explain how sound travels through air.
Air is a substance just as the dental floss or fishing line between the cups is a substance.
To see how well your young scientists are understanding the properties of sound, challenge them to explore the properties of their paper cup telephones further by designing new experiments. Try using your telephone with someone holding the line in the middle. All they'll need to do is replace the line between their cups with one that's three times as long. Then ask them to stand as far as the line will allow, again making sure that the line is taut. As one partner puts the cup to one ear, the other can shout while holding the cup on the other end of the line about six inches in front of his or her mouth.