When a bus starts moving suddenly the passengers tend to fall backwards. Why?
Answer: The tendency of a stationary object to remain stationary forever is called the inertia of rest. When a car starts moving suddenly, the passenger sitting in the car leans backwards. This happens because of the inertia of rest. When the vehicle is stationary, the passenger is also stationary.
When the car suddenly starts moving, the lower part of the passenger’s body moves as it is adjacent to the car. But the upper body wants to stay still under the influence of inertia. So the passenger leans back.