NCERT Solutions for Class 9 Science Chapter 9
Force and Laws of Motion
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Intext Questions
Page No-118
Questions No-4
Why do you fall in the forward direction when a moving bus brakes to a stop and fall backwards when it accelerates from rest?
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Due to the inertia of the passenger
Everybody tries to maintain its state of motion or state of rest. If a body is at rest, then it tries to remain at rest. If a body is moving, then it tries to remain in motion. In a moving bus, a passenger moves with the bus. As the driver applies brakes, the bus comes to rest. But, the passenger tries to maintain his state of motion. As a result, a forward force is exerted on him.
Similarly, the passenger tends to fall backwards when the bus accelerates from rest. This is because when the bus accelerates, the inertia of the passenger tends to oppose the forward motion of the bus. Hence, the passenger tends to fall backwards when the bus accelerates forward.
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Braking Scenario:
– Inertia’s Role: Imagine you’re on a moving bus. You and the bus are moving at the same speed.
– Abrupt Braking: When the bus stops suddenly, it slows down, but due to your body’s inertia, you want to continue moving forward.
– Result: Your body momentarily maintains its forward motion, causing you to lean or lurch forward relative to the bus.
Acceleration Scenario:
– Inertia’s Influence: At the bus’s initial rest, you are stationary.
– Quick Acceleration: As the bus accelerates forward, your body resists this change in motion.
– Outcome: Your body lags behind the bus’s acceleration, resulting in you leaning or falling backward relative to the bus’s direction.
Conclusion:
This experience is due to inertia, which tends to keep your body in its initial state of motion. When the bus abruptly changes its motion, your body tends to stay in its initial state, causing the sensation of leaning or falling in the opposite direction.