Kengo Yamada remembers asking a class of kindergartners where they thought wind came from. “One said, ‘Trees make wind,’” says the associate director of early childhood education at New Jersey’s Liberty Science Center. When Yamada asked the child why he thought that, the child said, "Well, I was walking outside and I saw the trees shaking, so they must make wind.”
Although the kindergartner wasn’t quite on the mark, Yamada says that child was starting to make sense of the world in a scientific way. And weather is actually an easy way to get kids wondering about science. (These experiments will teach kids about lightning, rain, and more.)
“They don’t have to conceptualize what wind, snow, or rain is,” says Ivory Williams, vice president of STEM teaching, learning, and innovation at Liberty Science Center. “They can touch it and taste it.”
And that can spark interest in science all around. “If you’re taught to notice a phenomenon, then you see it happening in a lot more places,” says Shaunna Donaher, a meteorologist at Emory University’s Department of Environmental Sciences.
Here are some experiments to show your young scientist how winter weather works.
HOW WIND FORMS
• Two empty glass or plastic bottles of the same size
• Hot and cold water
• Red and blue food coloring
• One playing card
• Towels, in case of spills
What to do: Fill one bottle with hot water (not too hot to touch!) and the other with very cold water. Be sure each one is filled to the brim. Add several drops of red food coloring to the hot water, and several drops of blue food coloring to the cold water.
Press the playing card against the mouth of the hot-water bottle. Turn the bottle upside down so it’s mouth-to-mouth with the cold-water bottle, then carefully slide out the playing card. The hot red water will not mix with the cold blue water.
Keeping the bottles attached at the mouth, carefully turn them over so the blue bottle is on top. The hot red water will rise as the cold blue water sinks, creating purple water. (Tip: Save the colored water for the next experiments!)
Cool science: This experiment uses water to show how wind currents move. “Wind forms because of uneven heating [in the air],” Donaher says. “Uneven heating creates pressure differences, and that will set the air in motion.” Hotter, less dense air rises (just like the hot red water) while colder, more dense air sinks (like the cold blue water). The warmer air is less dense, Donaher explains, because its molecules are moving faster and they’re farther apart. As lower-pressure, hotter air moves up, cooler air whooshes in to take its place. We feel that as wind.
If you can’t feel wind, that’s because warm and cool air aren’t mixing, just like when the hot water bottle was on top of the cold bottle. “When the atmosphere is stable (like the hot water on top), or if we don’t have pressure differences between locations, then we won’t have any wind,” Donaher says.
HOW WATER FREEZES
• A clear drinking glass (plastic will work, too)
• Masking tape
• Food coloring (or reuse the colored water from the previous experiments)
What to do: Pour some of the colored water into the glass and mark its level with a strip of tape. Place the glass in the freezer. Remove the glass when the water is completely frozen, then remeasure the water level and notice the difference.
Cool science: “When substances are cooler than their melting point, molecules move very slowly and can end up locked together in a structure that’s firm,” Donaher says. “This is what we call a solid. As the molecules move slower, there is more attraction between molecules so they can become ‘locked’ into a rigid structure.”
For a lot of materials, the colder it is, the less space it takes up. For instance, freezing melted wax will make it shrink so it easily pops out of a candleholder. “But water actually takes up more space when it freezes,” Donaher says. Why? “It's the way the water molecule bonds. It bonds at a kind of unusual angle,” which makes ice take up more space than water. (Read more about that weird angle in the snowflake experiment below.) That’s why the ice expands to a higher level than the water did.
HOW ICICLES FORM
• A paper cup
• A taller, narrower container, such as a reusable sports bottle
• A skewer or pen to make a pinhole
• Food coloring (or reuse the water from the previous experiment)
• Several inches of string
• A bead that slides onto the string
What to do: Make a pinhole on the bottom of the cup. Tie a knot in one end of the string, then thread the unknotted end through the hole so the knot is inside the cup and the string hangs out the bottom of the cup. Tie the bead to the bottom of the string. Wet the string and bead. Place the cup-and-string inside the bigger container. If the bead touches the bottom of the bigger container, pull up the string and knot it again so that the bead is suspended.
Dribble a few drops of colored water into the small cup and place the whole contraption in the freezer. After 15 minutes, add a few more drops of colored water. Repeat every 15 minutes until you can see an icicle forming at the bottom of the string.
Cool science: “Icicles form when droplets of water freeze as they’re being pulled downward slowly by gravity,” Donaher says. “Icicles usually grow in length over time as little bits of water melt, travel down the ice, and then refreeze.” In this experiment, droplets of water are going through the pinhole in the cup, traveling down the string, and freezing on the bead.
But why doesn’t an icicle form in the shape of a cylinder? As water continues to travel down the icicle, it releases heat. While you might think that would make the icicle at the top melt, it really acts as an insulator, which keeps in the cold. Because warm air rises, it insulates the top part of the icicle more than the tip, allowing to top to stay frozen and therefore wider than the bottom. Explains Williams, “More heat escapes from the tip, so the tip grows thinner and more quickly than the top, creating the long icicle shape.”
HOW SNOWFLAKES FORM
• Clear drinking glass
• Spray bottle of water or wet cloth
• Piece of black paper
What to do: Mist or wipe the glass with water. Place the glass in the freezer. After about an hour, when it’s covered in frost, take out the glass. Place the glass against the dark paper so you can see the frosty flakes on the surface. Let kids discover different shapes with a magnifying glass. (Tip: If you don't see frost, let the glass freeze longer.)
Cool science: High in the clouds, water vapor is attracted to what are called aerosols—particles of dust, smoke, or salt spray from the ocean— according to Donaher. If the cloud is 5˚F or colder, the water vapor will turn into ice crystals—what we know as snowflakes. In this experiment, the glass replaces the aerosol substances, giving the vapor something to cling to.
“Snowflakes will form with six sides or six points,” Donaher says. That’s because the two hydrogen molecules and one oxygen molecule (aka H2O) are positioned in a way that form a triangle. When those triangles freeze together, they form hexagonal shapes like a classic snowflake pattern. But they can also become a plate, column, or needles, depending on the temperature and humidity of the air, Donaher explains.