Question 13 Marks
Molecules in air in the atmosphere are attracted by gravitational force of the earth. Explain why all of them do not fall into the earth just like an apple falling from a tree.
Answer
View full question & answer→The air molecules move randomly as they possess thermal (temperature) energy. Air molecules and apples both are attracted by the earth by gravitational force but the resultant velocity of an air molecule is not exactly downward as in case of an apple (as apple has no other direction of motion except downward).
According to the second law of kepler’s the areal velocity of planet around the sun is constant.$\frac{\text{dA}}{\text{dt}}=\frac{\text{L}}{2\text{m}}=\frac{\text{r}\times\text{p}}{2\text{m}}=\frac{\text{r}\times\text{mv}}{2\text{m}}=\frac{1}{2}\text{r}\times\text{v}$
where, L is the angular momentum and M is the mass of the earth. But angular momentum$\vec{\text{L}}=\vec{\text{r}}\times\vec{\text{p}}=\vec{\text{r}}\times\text{m}\vec{\text{v}}$