Introducing the Scientific Method: How Many Water Drops Fit on a Penny?

To introduce the scientific method, I have my students perform an experiment that answers this question:  How many water drops fit on a penny?  Before reading on any further, make your own hypothesis.  After you have done that, continue reading!

I came across this activity years ago and have used it successfully many times.  This lab activity is quick and easy which makes it a great introductory experiment.  Students are able to make hypotheses, perform an experiment, collect data, analyze results, and begin drawing conclusions.  To perform this experiment, you will need the following materials:

  • pennies (1 for each student or group depending on class size)
  • droppers (1 for each student or group)
  • small cup of water
  • paper towels or tray to set penny on
  • notebook and pencil to record results

Before announcing the question to be answered, I always remind students that I do not want them to announce their hypotheses.  I don’t want their guesses influencing others’ ideas.

I then ask the question that we are attempting to answer and students record their hypotheses in their lab notebooks.  (Some students will ask how big the drops are, so you may need to show them the dropper and squeeze a few drops out onto a paper towel or into a cup so they can make an educated guess.)  If needed, divide students into groups and then distribute materials.

Students then place the penny on a paper towel or tray, fill the dropper with water, and count the number of drops that can fit on the penny before the water runs off.  Record results from each trial.  Repeated trials make results more reliable so allow students plenty of time to repeat the experiment.  Just make sure they start each trial with a dry penny.

Students are usually very impressed with the number of water drops that fit on a penny.  I have found that this one simple experiment often leads students to begin asking more questions.  What happens with other liquids on a penny?  Does it matter if the penny is turned to heads or tails?  How many drops would fit on a dime or quarter?  There are so many ways to extend this project if time and interest allow.  Use this as an introductory experiment or a lab during a study of water molecules.  Either way, it is an easy, engaging activity that students really enjoy.

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