The terminal velocity of a rain drop is 9 m/s. That means from the moment a drop leaves the cloud, its velocity increases continuously from 0 m/s to 9 m/s. But after that it stays constant. It travels all the way through the atmosphere with this 9 m/s velocity and hits the earth. This is a wonderful phenomenon. Had it not been like that, if the rain drop continues to gain speed, no living creature can tolerate its momentum. It will shoot like a tracer bullet and will shatter anything that comes in its way.
Hinduism explained this concept like this. Though there is water on earth, there was no rain for a long time from the beginning of the creation. Sage Bhageeratha did arduous tapasya to please Lord Brahma (the creator) to send Ganga (rain) to earth. Pleased by Bhageeratha's tapasya, Brahma agrees to send Ganga. But raises a question. He says, "My creation will not survive the momentum of Ganga. Her ferocity will shatter everything on earth. So I suggest you pray Lord Shiva - The all powerful supreme master to help you in reducing Ganga's ferocity while coming down to earth.
Bhageeratha is determined and focused on getting Ganga down onto earth. So he continues his tapasya to please Lord Shiva. Shiva - The kind hearted appears in front of Bhageeratha and offers himself to help. He orders Ganga to jump on to his head there by he will first absorb all the impact and then slowly release the water to earth.
But Ganga is headstrong and adamant. She did not realize the power of Shiva - the supreme. She decides to jump onto Shiva's head with full vigor and take him down and shatter everything. Shiva realizes Ganga's intention. He signal's her to jump from the sky. Shiva was standing on the earth with knees bent and hand on the hips to brace for the impact. Ganga hits Shiva's head. Shiva quickly locks her up in his tumultuous hair and captivates her completely. Then Ganga realizes about Lord Shiva and prays him to release her. Then Shiva releases Ganga slowly. Ganga flows down along Shiva's long hairs and reaches earth.
The philosophy behind this story is the science explained in the first paragraph. Shiva is also called as Vyoma Kesha. Vyoma means sky. Kesha means hair. Vyoma Kesha means he who has sky as his hair. Means he is spread across the sky as atmosphere.
Vyomakesha is not just another name of Lord Shiva. It is a scientific term. Gangavtaranam is not just story in Ramayana. It is a detailed explanation of the concept behind the terminal velocity of a raindrop.
