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

Explanation

The escape velocity of moon is 2km `//`s. The root mean square velocity (r.m.s.) for hydrogen is 2km`//`s . Thus hydrogen can easily escape from the moon.s atmosphere. Further, the molecule of other gases having high velocity will also leak from its atmosphere . Hence moon has no atmosphere. Similarly for other smaller planets.