State Newton's three laws of motion.

First Law (Inertia): Objects remain at rest or in uniform motion unless an external unbalanced force acts. Second Law: F = ma (force equals mass times acceleration). Third Law: For every action, there is an equal and opposite reaction acting on a different object.

What is momentum and what is the law of conservation of momentum?

Momentum = mass × velocity (p = mv), unit is kg·m/s. Law of Conservation of Momentum: The total momentum of a closed system remains constant if no external force acts. Example: m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂. This explains rocket propulsion and why a gun recoils when fired.

Why does a person sitting in a moving bus jerk forward when the bus stops suddenly?

This is due to Newton's First Law (inertia of motion). When the bus stops suddenly, the bus's velocity becomes zero. But the passenger's body, due to inertia, tends to continue moving at the original velocity — so it jerks forward relative to the bus.

Newton's Laws of Motion

Force and Laws of Motion • Class 9 Science • NCERT • CBSE

Newton's three laws of motion describe how forces affect the motion of objects. First law: An object at rest stays at rest unless acted upon by a force. Second law: F = ma. Third law: Every action has an equal and opposite reaction.

Key Formulas

p = mv (Momentum = mass × velocity)
F = ma (Newton's Second Law)
Impulse = F × t = m(v − u)
Conservation of momentum: m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂
1 Newton = 1 kg·m/s²

Frequently Asked Questions

State Newton's three laws of motion.: First Law (Inertia): Objects remain at rest or in uniform motion unless an external unbalanced force acts. Second Law: F = ma (force equals mass times acceleration). Third Law: For every action, there is an equal and opposite reaction acting on a different object.
What is momentum and what is the law of conservation of momentum?: Momentum = mass × velocity (p = mv), unit is kg·m/s. Law of Conservation of Momentum: The total momentum of a closed system remains constant if no external force acts. Example: m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂. This explains rocket propulsion and why a gun recoils when fired.
Why does a person sitting in a moving bus jerk forward when the bus stops suddenly?: This is due to Newton's First Law (inertia of motion). When the bus stops suddenly, the bus's velocity becomes zero. But the passenger's body, due to inertia, tends to continue moving at the original velocity — so it jerks forward relative to the bus.

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