Let’s talk about the weather. The weather affects us all, what we wear, what we eat and drink, and what our homes are like. Weather even helps to shape our landscape. The weather is with us all the time, whether it is hot or cold, windy or still, wet or dry. These experiments will help kids learn a little about how temperature, wind and humidity affect the weather.
WATER IN THE AIR
Moisture in the air, humidity, is one part of the water cycle. The main source of water comes from the earth’s five oceans and from lakes and rivers. But how does the water get into the air?
Take two jars of the same size and fill them with the same amount of water. Cover one of the jars with a lid and leave the other open. Set the jars next to each other and leave them overnight.
The next day, there will be less water in the jar left open. The water turned into water vapor, an invisible gas. This process is called evaporation. This is how water gets into the air.
How does the sun affect the evaporation of water in the air? Half fill two dishes with water. Place one in the sun or near a heater; place the other in the shade. Which one dries faster?
The warmer the water, the faster the molecules move into the air and the faster they evaporate. As the air temperature increases, it can hold more water. As it gets colder, it holds less and less.
EVAPORATION COOLS THE AIR
Liquids use heat to evaporate, so any place where evaporation takes place becomes cooler.
Set a thermometer out in the wind. If the air is still, use a fan. Note the temperature after 30 minutes. Use an eyedropper to dampen a small piece of cotton and wrap it around the bulb of the thermometer. Secure the cotton with a rubber band. Leave the thermometer in the wind and note the temperature again in 30 minutes. The temperature of the thermometer with the wet cotton will be several degrees cooler due to evaporation.
WATER COMING OUT OF THE AIR
Remove the label from an empty tin can and fill the can with ice water and a few drops of food coloring. Let the can stand on the table for five minutes.
Drops of water will form on the outside of the can. Since the drops are clear and not colored like the water inside the can, the water must be coming from the air. The water forms on the outside of the can as water vapor in the air around the can cools. As the air molecules slow down, the water changes from a gas to a liquid form through a process called condensation.
Water vapor is a part of warm air. As the warm air rises into colder and colder temperatures, the cold air can’t hold as much water vapor. Little drops of water begin to collect on dust particles as the air cools. This forms clouds. When the water drops are large enough they fall to the earth as rain or snow.
The movement of water from evaporation to condensation is called the water cycle.
HOW FAR AWAY IS THAT STORM?
Lightening and thunder happen at the same time but because light and sound travel at different speeds, they reach us at different times. Light travels at 186,000 miles (300,000 km) per second and takes a fraction of a second to reach us. Sound takes about 5 seconds to travel one mile (3 seconds for a kilometer).
When you see a flash of lightening, count the number of seconds until you hear the thunder. Divide that number by 5 (3 for kilometers). That will give you rough estimate of how far away the storm is. When you see the lightening and hear the thunder at about the same time, the storm is right above you.
This simple series of experiments will get kids thinking about the weather and what causes it. Next time they talk about the weather, they will have a lot more to say.