Explain why a) there is no atmosphere on moon b) there is a fall in temperature with altitude
(a) As acceleration due to gravity on moon is 1/6th of g on earth. So, the escape velocity on moon Ve=2gR=2.38km/s M= Mass of hydrogen As H2 is lightest gas m=1.67×10−24kg vrms=m3KBT =1.67×10−243×1.38×10−23×300=2.72km/s Due to small gravitational force and vrms is greater than escape velocity so molecule of air can escape out As the distance of moon from sun is approximately equal to that of earth so the intensity of energy of sun reaches to moon is larger due to lower density of atmosphere, distance become smaller than earth when moon is towards sun during its rotation around earth Due to this (sunlight), rms speed of molecule increase and some of them can speed up more than escape velocity and so probability of escaping out increased hence over a long time moon has lost most of its atmosphere (b) The temperature of atmosphere is due to the kinetic energy of air molecule Due to lower atmospheric pressure at higher altitude molecules of air rises up so their potential energy increase in turn the kinetic energy decrease results the decrease in temperature. Due to lower atmospheric pressure at higher altitude the gas expands and gives cooling effect and so decrease the temperature
