Defy gravity and show your students some magic by performing this drops of water on a coin science experiment. We added an extra dimension to this classic 5 minute science experiment by comparing how many drops of water fit onto each coin (penny, nickel, dime, and quarter) and tracking the data on a table to add a more mathematical and scientific element to it.
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I started this 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.
Drops of Water on a Coin Experiment
The kids followed these instructions to complete the drops of water on a coin experiment:
- 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:
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.