Explain why
(a) there is no atmosphere on moon
(b) there is fall in temperature with altitude

Explanation

(a) gravitational force of moon is roughly `1/6 th of the gravitational force of earth. Therefore, escape velocity of air molucules on moon is smaller than that on earth.
Since moon is in proximity of earth, as seen from the sun, therefore, moon rececive almost same amoumt of heat per unit area as does the earth. A large number of molecules on moon have speeds greater than escape velocity on moon, and therefore, they escape. the rest of the molecules arrange the speed distribution for the equilibrium temerature. again, a significant number of molecules escape as their speeds exceed the escape speed. hence, over along period of time, moon has lost most of its atomsphere.
(b) as molecules move higher, their potential energy increases and hence KE decreases. The temperature falls. At greater height, more volume is available. the gas expands and hence cooling occurs.