We have, Newton's first law: It states that " Every body continues in its state of rest or of uniform motion in a straight line unless compelled by an external unbalanced force to change that state". According to first law, a body by itself cannot change its state of rest or its uniform velocity. This is the property of all materials and is called inertia. Due to this inertia, passengers standing in a bus will have a tendency to be in their initial position and are thrown outwards when the bus take a sudden turn.