We cannot walk on ice because of reduced frictional force.Ice is also very smooth. Smooth surfaces have reduced friction while rough surfaces have a lot of friction.Friction is also known as a necessary evil because it is very necessary in life but causes harm in form of wear and tear. It also produces heat. Some good examples of friction are: a) rubbing of hands b) ball stops after moving for a while Ice skaters have special blades for skating on ice. There skates have blades that cut the ice and make a strong grip to let them skate.
Whenever we throw a ball up in the air, it falls back to the ground . This is because of a force called gravitational force or gravity.This is the force in which all the objects are pulled towards the earth. Sir Isaac Newton was the first man to discover it.
Invent means "create or design [something that has not existed before ]". According to the recent history Vasco da Dama was the first European to reach India by sea linking Europe and Asia for the first time ocean route , was accomplished on his first voyage to India .[1497-1499] , so you can say that he discovered India .