Estimated read time: 3-4 minutes
This archived news story is available only for your personal, non-commercial use. Information in the story may be outdated or superseded by additional information. Reading or replaying the story in its archived form does not constitute a republication of the story.
Low-pressure zones create clouds because the rising hot air carries moisture with it. The moisture is in the form of a gas called water vapor. When the water vapor cools, it forms water droplets that join together to form clouds. How does the water vapor get into the air in the first place? Most of it comes from evaporation. Evaporation happens when water molecules warm up - they gain enough energy to change from a liquid into a gas, and then they rise up into the air to be carried on rising convection currents. You have seen this happen in your kitchen when steam rises from boiling water.
Are there factors that can change how fast water evaporates? You can find out by setting up an experiment to test the effect of wind, temperature and surface area on the rate of evaporation. The following procedure will give you the basics, but feel free to come up with your own methods of testing and measuring the results. This kind of experiment would make a great science fair project. (Be patient: some of these tests can take more than one day!)
* two kitchen sponges (they should be the same size)
* electric fan
* small glass or beaker
* pie pan or shallow dish
Question & Hypothesis: How do factors such as wind, temperature, and surface area affect the rate of evaporation? Will wind or heat cause water to evaporate faster? Will a greater surface area speed up or slow down evaporation? Write down your predictions.
- Test the effect of temperature using an incandescent lamp to provide heat. Place two kitchen sponges on plates and pour 1/8 cup (C) water over each of them. (Depending on the size of the sponge, you may need to use a bit more water. Use enough to get the sponge wet all the way through.) Place one of the sponges directly under a lamp and the other at room temperature out of direct sunlight. Observe the sponges at regular intervals, and reduce the time between observation as they get nearer to drying. Record how long it took for each sponge to dry completely. Which sponge dried faster?
- Test the effect of wind using an electric fan. Wet the sponges as you did in step 1. Set one sponge 12 inches away from an electric fan and turn the fan on. Set the other sponge some place out of the draft. Observe the sponges at regular intervals. Record how long it took for each sponge to dry completely. Which one dried faster? Did the sponge in the fan dry faster than the one under the lamp in step 1?
- Finally, test the effect of more or less surface area. Pour 1/8 C water into a small glass. Find the surface area of the water in the cup using the equation Ï€=r ² (Ï€ = 3.14, r = radius. Find this by measuring the diameter of the cup and dividing this by two). Pour 1/8 C of water into a pie pan or wide shallow dish. Measure the surface area of the water in this container. Set the cup and the pan on the counter and check them a few times a day. Which water evaporates faster - the water with the small surface area or the large surface area?
Conclusions: Were your predictions correct? Which speeds up evaporation more, wind or heat? Based on your results, do you think the temperature or speed of wind would affect the evaporation rate? Can you think of other factors to test or a more precise way to test these factors again?