Dear Amy: Why does rain form into drops? — Angela, Kuwait
Dear Angela: Water is everywhere! It covers about 70 percent of the Earth’s surface, and it’s even in the air you breathe. Although it’s a very common substance, water has many unique properties, including a high surface
tension. This means that molecules of water are “sticky” and like to cling together, causing them to clump into droplets rather than spread out. Want to see water’s surface tension in action? Predict how many drops of water will fit on a penny and then do the experiment at PBS Kids Zoom, pbskids.org/zoom/activities/sci/dropsonpennies.html, to find out if your guess was right.
Water vapor in the atmosphere condenses into liquid droplets to form clouds. When enough droplets combine, they can become heavy enough to fall back to the Earth’s surface as rain, sleet or other forms of precipitation. Did you know that raindrops aren’t shaped like tears? Small raindrops are spherical, but larger raindrops flatten at the bottom due to air pressure pushing on them as they fall. To learn more about water science and the water cycle, visit ga.water.usgs.gov/edu.
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