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Would you like to splash around in some water on these hot summer days? Try this activity and tell your mom you are doing a science experiment!
As drops are added, they gradually mound into a dome instead of just flowing off the penny. Each drop raises the surface of the dome, until it gets too big and breaks.
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a penny an eyedropper liquid detergent tap water paper towel a place to work that your parents won’t mind getting wet!
The dome shape is caused by surface tension .
Surface
tension is caused by the grouping of molecules. Under the surface of the water, each water molecule attracts and is attracted to molecules on all sides of it.
Wash your penny. Rinse it and dry it well.
Place the penny on a flat surface that’s okay to get wet.
Fill the eyedropper with water and slowly drop water onto the penny, one drop at a time. Count how many drops you can add.
The surface molecules are attracted to the molecules below and to the sides, but there is nothing above the surface molecules to pull upward. The surface molecules pull together and act like a “skin” on the surface of the water.
Molecules pull together on the surface
Water molecules attracting from all sides
Standards Link: Physical Science: Students know that matter has different states (i.e., solid, liquid, gas) and that each state has distinct physical properties.
What shape does the water take? Repeat three times and find the average number of drops the penny can hold.
Repeat this experiment with cold water and then with hot water. Does the temperature of the water change the number of drops that fit on the penny?
Add a drop of soap to the water. Does this change the number of drops that fit on the penny?
The largest hailstone ever recovered in the United States, a seven-inch (17.8- centimeter) wide chunk of ice almost as large as a soccer ball, was found in Aurora, Nebraska.
Try this same activity with di erent liquids such as cooking oil, rubbing alcohol, liquid detergent, salad dressing, etc. Compare how many drops of each liquid t on the top of a penny. Standards Link: Nature of Science: Students understand the nature of scientific inquiry (using tools, making observations, recording notes).
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© Vicki Whiting June 2024
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