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)
Free printable table to keep track of the results! (Remember to change the page orientation to landscape before printing.)
- 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?
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.
Original article and pictures take http://www.sciencekiddo.com/2015/01/surface-tension-drops-of-water-on-coin.html site