Kindergarten, Science, Week 38

Continuing with The How and Why Book of Weather

• Hot air rises
• Experiment: Remove the shade from a table lamp that has an incandescent light bulb. Turn the bulb on and let it sit for about ten minutes. Then stick your finger in corn starch (so that just a little is on your finger) and flick it at the light bulb. The light bulb heats up the air around it, causing the air to rise. The powder from the corn starch allows you to see the air rising.
• Why hot air rises
• When air heats up the molecules move faster, bumping into each other more, so they move farther apart.
• Because the molecules are farther apart, the air is lighter, so it rises.
• Experiment: Blow up a balloon and tie it. Measure around the largest part of the balloon. Set the balloon in the sun for about ten minutes. Measure the balloon again. The balloon should be bigger.
• We tried this first with white and pink balloons because they were the easiest at hand. When they did not get larger, I searched for a balloon that was a dark color. It worked! So this experiment can also show that light colors reflect heat and dark colors absorb heat.
• The earth does not heat evenly
• Experiment: Put a bowl of dirt and a bowl of water in the sun for about thirty minutes. Take the temperature of the surface of the dirt and the surface of the water. If you don't have a thermometer to use, your child should be able to tell the difference just by feeling them.
• Water does not heat as quickly as land
• Why breezes blow
• As the land heats up, the air above it heats up and rises. The cooler air over the water rushes in to take its place. This is called an onshore breeze.
• At night, when the sun goes down, the land cools off faster than the water. This is because only the surface of the land has been heated, but the sun's rays go deep into water and heat it to a depth of several feet.
• Now the water is warmer than the land. The air above it rises and the cooler air from over the land rushes in to take its place. This is called an offshore breeze.
• Water you can't see
• When a puddle dries up, the water molecules have jumped up into the air. We say the water has evaporated. Water carried by the air is called water vapor.
• Heat causes water to evaporate.
• Experiment: Take two saucers and put a teaspoon of water on each. Place one in the sun and one in shade. The water in the sun should evaporate faster.
• Wind helps speed evaporation.
• Experiment: Wet a paper towel. Tear it in half. Place one half where the air is still. Put the other half in a breeze (you can use a fan). Which dries faster?
• More water will evaporate from a large surface than a small one.
• Experiment: Put a spoonful of water on a saucer and then fill the spoon again and leave that water in the spoon. The water on the saucer should dry up faster.
• The water cycle
• Experiment: Take a glass and set it over some grass or small plants. They should be in the sun. A watery film begins to form on the inside of the glass. (I was surprised at how quickly it happened.) Molecules of water from the grass/plant and soil have evaporated and become water vapor. When some of them hit the cooler glass they form fine drops of water.
• The first step in the water cycle is evaporation. Water from the grass and soil evaporated inside the glass.
• The second step is condensation. We can see this as clouds or fog. The water vapor in the glass condensed on the inside of the glass.
• The third step is precipitation. When water returns to earth as rain or snow. If you leave your glass over the grass for a longer period of time, larger drops of water should form and fall back to the ground.
• What is a cloud?
• When air becomes cooler, water vapor condenses around particles of dust (etc.) floating in the air. Millions and millions of droplets are formed high in the sky and they cluster together in groups. These are the clouds we see.
• Sometimes clouds look bright and puffy because the sun is shining through them.
• Sometimes the sky looks like one big gray cloud because there are so many layers of clouds that they block out the sun's rays.
• Sometimes the clouds form very high in the sky where it is much colder, and the droplets freeze. These clouds look like wispy ribbons.
• When water droplets form at ground level, it is called fog.
• Dew and frost
• At night, when the land cools off, some of the water vapor in the warm air condenses on the cooler plants, rocks, soil, playground equipment. This is called dew.
• On very cold nights the water vapor condenses directly into ice crystals and form a white film over the ground and house roofs. This is called frost.