Water, Water, Everywhere We are surrounded by water, and use it every day -- to drink, to cook with, to flush our toilets and wash our dishes. 70 percent of the earth's surface is water. That's a lot of water, isn't it! Another cool thing about water is that it recycles itself. Most of the water on the earth today has been around for millions of years. It continually evaporates (changes from liquid to gas) and condenses (changes from gas to liquid). In other words, the rain falling from the sky has fallen millions of times before and will fall millions of times again. We usually think of water in its liquid state--the water that flows from our taps and rivers, makes up our lakes and oceans. But water comes in two other forms: solid, like ice and snow; and as a gas. The temperature of the water determines its physical state. At 32° Fahrenheit (0° Celsius) and below, water freezes into its solid form (ice). Above 32° F, water remains a liquid. In its liquid form, water continually evaporates. Tiny, invisible droplets break off from the liquid mass and float into the air. The warmer the temperature of the water, the faster the droplets break off and the more quickly the water evaporates. That's why rain puddles dry up faster on hot days. When the water temperature reaches 212° F, water boils. In boiling water, the invisible droplets break off so quickly that they form bubbles in the water that rise to the top and release the vapor (the invisible droplets) into the air. Have you ever seen mist sitting over a lake or field, or steam rising from a hot bath and wondered why it was there? Well, when water vapor hits cooler air, the invisible droplets start clinging together until they become big enough for our eyes to see, but they remain small enough to float in the air. The mist hovering over a lake or field is very much like a cloud in the sky. Clouds are gatherings of water droplets that have evaporated from the earth. As temperatures cool, more and more droplets gather combine until they are too heavy to keep floating in the cloud. Then they fall from the sky and we have rain. If the air temperature is lower than 32° F, the droplets will keep condensing until they turn into snow. Experiment with this concept!Evaporation ExperimentEvaporation requires energy, and heat is a form of energy. So as tiny droplets break away from their source--such as a puddle, hot bath, or sweat on your skin--they take heat with them. Humans sweat to keep cool. When you get hot, your body releases sweat through tiny holes (pores) on your skin. The sweat then evaporates into the air, taking heat with it, and cooling the body. Fun Fact: Though humans are not the fastest runners, we can run for a much longer period of time than most animals. We are able to because our bodies sweat to keep from overheating. If we didn't perspire we'd have to rest more often to let our bodies cool down. Of course, we have to drink water if we sweat a lot, or else our bodies will run dry (dehydrate). Have you ever noticed that dogs hang their tongues and pant when they are hot? That's their way of keeping cool: the water on their tongues evaporates. Think of how much cooler they would be if they could evaporate water from their entire bodies like humans can! WANT SOME PROOF?It's always a good idea to test the information someone gives you so you can see for yourself if it is true. We have provided you with an experiment you can do at home to test the information we gave you here! MAKE YOUR OWN REFRIGERATORMATERIALS:
WHAT TO DO:
HOW IT WORKS:As water evaporates from the clay pot, it takes heat away with it so the soda underneath stays cool. The bowl of water keeps the clay pot wet so that your "refrigerator" lasts longer. WHAT DO YOU THINK?Can you think of other uses for water evaporation? Does this experiment help you understand how your sweat keeps you cool? |
