We tend to fall backwards due to inertia. When the bus suddenly starts moving, our body initially remains at rest while our feet, in contact with the floor, move with the bus, causing a backward motion of our upper body.

Safety belts exert a force on our body, slowing down its forward motion, thus preventing injuries by reducing the impact of collision.

A sudden application of brakes may cause injury due to the inertia of our body, causing it to move forward and collide with the panels in front.

We tend to remain at rest due to inertia, as described by Newton’s first law of motion.