i can explain this answer in hindi well. But, i think you are learning hindi, thus i will try to write in english. See, this religious act started with teacher-student relation. when a student used to touch his teacher's feet then, he gives all his bad habits to teacher and takes positive energy from teacher. A teacher will never touches his students feet. THus a young person touches his elder's feet. It shows dedication of elder people that they take negative energy from their youngers and still they feel happy. this is our hindu culture, to give happiness to others. we dont want hatred. only love and peace everywhere.

people in India greet one another by touching the feet of the other person because its symbol of respect & honour which is in our heart for other person. and its our tradition which was followed by our ancestor since starting of indian culture.

First of all, its a MARK of respect. U (not exactly) touch elder's feet to get blessings. Its the same ritual which u follow in Church. U bend / sit in front of the God and on behalf of Jesus Christ, the Priest BLESS U. Second scientific approach is, When u bend and touch feets, the RECEIVER / elder touches YR head. Put the hand on yr head. In the process POSITIVE energy passes thru RECEIVER (in this case the person who bends) and his / her hands. This positive energey is like some form of Rays which cant be seen with naked eyes. Is it clear ? Please feel free to ask any further explanation, if required.

it's our culture.but not compulsory.it is a symbol of respect.it depends on person to person.