A
HOW WIND FORMS
You'll need:
·Two empty glasses or plastic bottles of the same size
·Hot and cold water
·Red and blue food coloring
·One playing card
·Towels(毛巾), in case of spills
What to do:
Fill one bottle with hot water 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.
Cool science:
This experiment uses water to show how wind currents move. "Wind forms because of uneven(不均衡)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.
21. What material does the science experiment need?
A. Cloth to keep warm. B. Two playing cards.
C. Different food coloring. D. Some colored water.
22. Where is the playing card placed during the experiment?
A. Around the two bottles. B. Between mouths of two bottles.
C. In the bottle with warm water. D. Below the bottom of one bottle.
23. What sets air to move to form wind?
A. Water pressure. B. Warmer air. C. Colder air. D. Air heating.
