Students conduct a simple test to determine how many drops of each of three liquids water, rubbing alcohol, vegetable oil can be placed on a penny before spilling over. Because of their different surface tensions, more water can be piled on top of a penny than either of the other two liquids. However, the main point of the activity is for students to come up with an explanation for their observations about the different amounts of liquids a penny can hold. To do this, they create hypotheses that explain their observations, and because middle school students are not likely to have prior knowledge of the property of surface tension, their hypotheses are not likely to include this idea. Then they are asked to come up with ways to test their hypotheses, although they do not need to actually conduct these tests as part of this activity.

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