Surface Tension | Drops of Water on a Coin + Free Printable

I am sure you have seen this experiment done before. Ya know, the one where you see how many drops of water you can fit onto a penny? We added an extra dimension to this classic experiment by comparing how many drops of water will 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. This is also fantastic fine motor skill practice for kids as they learn to use and control a plastic pipette!

Which coin do you think will hold the most drops of water? Make an educated guess before you begin. This is called your hypothesis.

Total Time: About 5 minutes
Safety Concerns: None.

Materials You Need:
A cup of water
A variety of coins (we used a penny, a nickel, a dime, and a quarter)
Plastic pipette
Free printable table to keep track of the results! (Remember to change the page orientation to landscape before printing.)

Directions:

• 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 your results on this free printable table! There is room to do three trials for each coin so you can average the trials together to see which coin holds the most water!

So why does a dome form when you drop water on 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.

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

So what were your results? Which coin held the most drops of water? Was your hypothesis correct? Why?

Like this article? Subscribe to our monthly newsletter! Enter your email address below.


powered by TinyLetter

*This post contains affiliate links. Please see our disclosure policy.
 

This post is part of the A-Z STEM Series. Every day during the month of January 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.