Coin and Water Experiment | Drops of Water on a Penny

Have you ever wondered how many drops of water can fit on a penny? Find out for yourself, defy gravity, and show your students some magic by performing the coin and water experiment. We added an extra dimension to this classic lightning-fast science experiment by comparing how many drops of water fit onto each coin (penny, nickel, dime, and quarter) and tracking the data on a free printable table.

If you enjoy doing fast science experiments like this be sure to check out our new science packet, 5 EXPERIMENTS IN 5 MINUTES! It comes loaded with colorful pictures, complete scientific explanations, more cool extension activities to try, PLUS no-prep science journal pages for each experiment! Click the picture below to find out more!

Drop of Water on a Penny

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I started this coin and water experiment by placing one of each coin (penny, nickel, dime, quarter) on a paper towel and asking the kids which coin they thought would hold the greatest number of drops of water. They each made a hypothesis, or an educated guess.

I printed out the chart available for free below so we could keep track of our results. Armed with a pencil to write with, a plastic pipette, and a cup of water, the kids were ready to begin.

Coin and Water Experiment

The kids followed these instructions to find out how many drops of water can fit on a penny and other coins:

• Set the coin on a flat surface.
• Fill a plastic pipette with water.
• Carefully squeeze out water drop by drop from the pipette onto the coin. Count how many drops fit on the coin before the dome breaks and the water spills over.
• Keep track of the results on the printable chart, available below. Repeat three times for each coin and then calculate an average in the last column.

What were the results? Which coin held the most drops of water? Was the hypothesis correct? Why or why not?

Surface Tension Explained

So why does a dome form when water is dropped onto the coin? And why does the dome eventually collapse?

The answer to this lies in the structure of the water molecule itself. Water is a polar molecule, meaning that it has a positive end and a negative end. The negative end of one molecule is attracted to the positive end of another molecule (similar to a magnet), which makes the molecules stick together tightly. The molecules on the surface are pulled inward and they stick together so strongly that they form a dome. This is called surface tension. Eventually, though, gravity overcomes this force and the dome breaks, spilling water over the sides of the coin.

Download a free printable chart to keep track of the results by clicking below:

For another fantastic (and colorful!) surface tension activity check out our magic milk fireworks! The kids will LOVE it.

This post is part of the A-Z STEM Series. Every day during the month we will be bringing you tons of awesome science, technology, engineering, and math activities to do with your kids! By the end of the month you’ll have over 50 STEM activities to keep your kids busy learning.