i'd say it would be galileo!
elastic collision : when two objects collide with each other then
(1). the kinetic energy is conserved
(2). the momentum is conserved
example : when we throw a ball on the floor then its bounce back.
inelastic collisions : when two object collide with each other then
(1). the momentum is conserved
(2). the kinetic energy is not conserved
example : car crash