doesn't know the 'ABCD' of studing

In hostel my roommates are tamilans. In the next room that room have for malayalees.In study times daily am there (only for chatting).There we will discuss many serious things about earth,Ghost,comparison of India with other countries etc..and etc..Yesterday one of my friend suggest that earth is in the shape of a bucket.He believed that the organisms are lived inside the bucket shaped earth.We tried to teach him, it is not like that earth is in the shape of an apple.In that time he come to have another doubt if it is like an apple then why we don't slips to atmosphere.In that time my another friend got the same doubt.Then teach them about gravitation force.Then that problem was solved....Now I only have doubt about gravitation force.