Question

(a) Fill in the blanks with appropriate words.
When air _______________(heats/cools), the air molecules _____________(spread out/come closer) so that there are fewer air molecules in the same space. _______________(Warm/Cool) air weighs less than _______________ (Warm/Cool) air, which means that warm air presses down on the earth less than cool air. Less pressing means _____________ (less/more) pressure. Thus, a mass of warm air creates an area of low pressure. Warm air rises and produces clouds. So, _______________ (low/high)pressure areas usually bring rain or storms.
(b) Now, explain how high pressure areas are associated with clear skies.

Answer 1

(a) When air heats, the air molecules spread out so that there are fewer air molecules in the same space. Warm air weighs less than cool air, which means that warm air presses down on the earth less than cool air. Less pressing means less pressure. Thus, a mass of warm air creates an area of low pressure. Warm air rises and produces clouds. So, low pressure areas usually bring rain or storms.

(b) The high pressure areas have slow-moving air and thus, clouds cannot be formed; therefore, such areas are associated with clear skies.