Question

Give reason that when a bus at rest starts suddenly, a standing passenger tends to fall backward.

Answer 1

Newton's first law states that an object will stay at rest (or in motion) unless acted upon by an unbalanced force. This principle is known as inertia, the property of an object to stay at rest or continue in motion unless disturbed. When a bus suddenly stops, the breaks have created an unbalanced force that quickly stops the motion of the bus, but have not changed your inertia. The only method by which the bus can stop a person is through friction, whether they are sitting in a seat or standing up. When the bus suddenly stops, your inertia has not been changed and you will continue in motion by moving forward until friction (or grabbing something) also stops you. The same principle is true for when the bus suddenly starts moving.