How Do Weather Conditions Affect How Fast a Puddle Evaporates?

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Problem:

How do weather conditions affect how fast a puddle evaporates? Does water evaporate faster on a cooler or warmer day?

Materials:

• Paper and pencil
• Large cup or small bucket of water
• Large, flat expanse of bare asphalt
• Stick of sidewalk chalk
• Timer or watch
• A few days with differing weather conditions
• Camera

Procedure

1. On a sunny day sometime around midday, go outside and write down (or have a helper write down) the date, the time, and your observations about the weather. How sunny is it? Is it warm or cool? How windy is it? Does the air feel dry or humid? If you can find out the temperature, humidity, pressure, and so on, write that down too.
2. Now pour the bucket of water out on the concrete so that it makes a puddle. Quickly draw around an outline of the puddle with the sidewalk chalk.
3. Wait five minutes, then look at the puddle. It should be smaller than it was five minutes ago. Trace its edges with the chalk again.
4. Keep doing this every five minutes until the puddle is completely gone or until an hour has gone by, whichever comes first. You should have a maximum of 13 puddle outlines, each smaller than the last.
5. Take a picture of your chalk outlines.
6. On a day when the weather is noticeably different from the first day (but not wet out or too cold for comfort), repeat steps 1-5. Try to use the same spot and take a picture from the same angle. Then do it again on yet another day when the weather is different—hotter, windier, cloudier. You’ll want at least three sets of observations, but do it as many times as you'd like!
7. Now put all of your observations and your pictures together. You should see that on some days there was more space between the puddle outlines—on those days, the water evaporated faster—and on some days, when the water evaporated more slowly, there was less space between the outlines. Try to figure out what was different on the days when the water evaporated faster. Did hotter weather make it evaporate faster or slower? What about wind? Did it evaporate faster or slower on a cloudy day? Did the time of day make a difference?

Terms/Concepts: evaporation, temperature, wind, humidity