Key Idea: Clouds and rain form as air cools and water vapor in the air condenses into water droplets.

Students are expected to know that:

  1. Air cools as it rises away from the surface of the earth. Air can rise when 1) its temperature increases, 2) it is pushed upward as it moves over landforms (e.g., mountainsides), or 3) when it is pushed upward as the air encounters cooler (i.e., denser) air that wedges underneath the warmer air.
  2. Clouds (including fog) can form anywhere that air cools. The lowering of air temperature can cause water vapor to condense such that the molecules of water that are part of the air form extremely tiny droplets of liquid water (or ice) in the air. The droplets that make up the clouds are not heavy enough to fall to the ground as precipitation.
  3. As more droplets form in a cloud they collect together to form larger and heavier droplets. The droplets can eventually become heavy enough to fall toward the ground as rain, snow, sleet, or hail. The form of precipitation depends on the temperature of the air around the droplet.
  4. The more water vapor there is in the air, the greater number of water droplets will form as the water condenses, making it more likely that visible clouds will form and that droplets will collect together and become heavy enough to fall as rain.
  5. The cooler the air becomes, the more water will condense and form water droplets, making it more likely that clouds will form and that droplets will collect together and become heavy enough to fall as rain.

Boundaries:

  1. Students are not expected to know the names and characteristics of specific types of clouds other than fog (e.g., they are not expected to know that some clouds are made of ice instead of water) or the conditions under which different types of clouds will form.
  2. Students are not expected to know the term “dew point.”
  3. Students are not expected to know that water droplets form around tiny solid particles of matter in the air or that droplets are more likely to form when there are more particles in the air.
Percent of students answering correctly (click on the item ID number to view the item and additional data)
Item ID
Number
Knowledge Being Assessed Grades
6–8
Grades
9–12
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WC089002

Clouds can form anywhere, even far from bodies of water, because air with water in it can move into an area and form clouds.

57%

58%

WC076002

Molecules of water can be found in clouds and in air far away from clouds.

52%

60%

WC079002

Clouds are made up of tiny water droplets that form as water vapor in the air condenses.

54%

54%

WC083002

It will not rain if the tiny water droplets that make up clouds are not heavy enough to fall from the clouds.

48%

53%

WC081002

As cool air moves toward warmer air, the cool air can push the warmer air upward, which causes the warmer air to cool, condense, and form clouds.

41%

51%

WC091002

Clouds are likely to form as air moves up over a mountain because air cools as it rises and clouds are likely to form as air cools.

40%

50%

WC085002

Rain falls when tiny water droplets in clouds combine to form larger droplets.

41%

44%

WC080003

Rain forms as the air in a cloud cools, causing tiny water droplets to form and combine to form larger droplets.

35%

42%

WC084002

Rain falls from clouds when air cools, causing water droplets to form.

31%

49%

WC089001

Clouds form anywhere there is moist air that cools to form tiny water droplets.

40%

32%

WC082003

If two places have the same amount of water vapor in the air, rain is more likely to fall in the place where the air is cooler.

24%

30%