Question

It is advised to tie any luggage kept on the roof of the bus with a rope.Why?

Answer 1

Every object has inertia due to which it tries to maintain its state of rest or state of uniform motion. Due, to inertia, any luggage placed on the roof of a bus gets a jerk when the bus moves suddenly from its state of rest. This will shift the luggage from its original place.
When the bus brought to a sudden stop, the luggage will move forward from its original position. Any piece of luggage placed on the roof of a bus but left untied is in danger of falling down and getting damaged or lost. Hence, it is advised to tie luggage with a rope, kept on the roof of a bus.