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

When the bus accelerates and moves forward, it acquires a state of motion. However, the luggage kept on the roof, owing to its inertia, tends to remain in its state of rest. Hence, with the forward movement of the bus, the luggage tends to remain at its original position and ultimately falls from the roof of the bus. To avoid this, it is advised to tie any luggage kept on the roof of a bus with a rope.

Because even though bus comes to rest, luggage are in motion, They fall down. So, it is tied with a rope to prevent falling.

(a) if the bus starts moving suddenly, thern due to its inertia of rest, the luggage kept on the roof of the bus tends to remain at rest and hence may fall down from the roof of the bus.
(b) if the moving bus stops suddenly, thenb due to its inertia of motion, the luggage kept on the roof of the bus tends to remain in motion and hence may fall down from the roof of a bus are tied with a rope, they cannot fall down when the bus starts suddenly or stops suddenly.

When the bus starts suddenly, the lower part of the luggage kept on the roof being in contact with the bus begins to move forward with the speed of bus, but the upper part tends to remain at rest due to inertia of rest. Therefore, the upper part is left behind and hence luggage falls backwardd. So, it is advised to tie any luggage kept on the roof of a bus with a rope.

Any luggage kept on the roof of a bus should be tied with a rope. This is because when the bus starts suddenly, the luggage pieces may fall down due to inertia of motion.