Air is matter and therefore it must take up space. This experiment dramatically illustrates the fact that an empty cup is truly not empty. It is filled with air.
2 plastic cups, 1 with a hole in the bottom
2 paper towels or tissues
Large beaker (1000 mL) or large pail
What To Do
Ball up a small piece of paper towel or tissue. Using double sided tape attach the towel or tissue to the inside bottom of the plastic cup without a hole. Fill the pail of water or beaker approximately half full. Ask students to predict what will happen to the paper towel when the cup is dunked upside-down in the water. Hold the bottom of the plastic cup. Push the plastic cup into the water with the open end of the cup pointing down into the water. Pull the cup out of the water. Have the students inspect the tissue or paper towel. Now do the same experiment, except with the cup that has the hole in the bottom. Ask students how this will change what happens to the paper towel when the cup is placed in the water. Try the experiment again.
1. Ask the students to tell you what happened to the tissue. Let the students tell you their ideas on why there was a difference between the condition of paper towel with and without the hole in the bottle of the cup.
When the tissue is added to the cup the remainder of the cup continues to be filled with air. When the cup is submerged, because air is compressible some water will enter the cup. But, because two types of matter cannot occupy the same space simultaneously, the compressed air serves as a barrier between the tissue and the water and the paper remains dry.
Ask the students to add more and more paper to the bottom of the cup until it becomes wet when submerged.
"Teaching Chemistry with Toys: Activities for Grades K-9." McGraw-Hill, Terrific Science Press, 1995. ISBN: 0-07-064722-4
© S. Olesik, WOW Project, Ohio State University, 1999.