Why Rainbow is in the form of an arc?

Why is a rainbow always bent in the shape of a semi circle…?? but according to the theory light travels straight….!!! (Ramesh asked)

What is the difference between centre of gravity,centroid and centre of mass ?

Centroid is the geometric centre of a plane figure or object Centroid divides the shape into regions of equal moments.     Centre of mass is the mean location of all masses in a system   Centre of gravity is the point through which the w...