36 The Atmosphere Conceptual Physics Text Correlation: Section 20.1
Why does a passenger jet flying at high altitude fly with more of a nose-up attitude than when it is flying at low altitude? Answer: At high altitudes there is not much air to "ride on." Consequently, an aircraft must push a greater volume of air downward. It does this by flying with more of a nose-up attitude so that the wings deflect the air down more strongly. Question 1
Why does a balloon expand when it ascends? Answer: It expands because there is less air pressure outside acting on it to keep it small. Question 2
Why do we not notice the weight of air? Answer: We don't notice the weight of air just as we wouldn't notice the weight of water in a plastic bag if we were submerged in water (see Figure 20.3 in the textbook). If we were on the moon, where there is no atmosphere, and a bag of air were handed to us, we'd notice its weight. Question 3 • Those steel gas bottles of compressed gases used in hospitals are noticeably lighter when they're empty.