Atmospheric pressure is equal to the weight of a vertical column of air, extending all the way up through the atmosphere, divided by the cross-sectional area of the column.
(a) Explain why that must be true. [Apply Newton's second law to the column of air.]
(b) If the air all the way up had a uniform density of 1.29 kg/m 3 (the density at sea level at 0° C), how high would the column of air be?
(c) In reality, the density of air decreases with increasing altitude. Does that mean that the height found in (b) is a lower limit or an upper limit on the height of the atmosphere?