Ch 9 introduces Newton's three laws of motion and the concept of momentum. Students learn to calculate force, momentum, and apply the law of conservation of momentum.
First Law (Law of Inertia): an object at rest stays at rest, and a moving object continues with same velocity unless acted upon by an external force. Second Law: F = ma (force = mass × acceleration). Third Law: for every action, there is an equal and opposite reaction.
Momentum p = mass × velocity (kg·m/s). Newton's 2nd law: F = Δp/Δt = m(v−u)/t. Conservation of momentum: total momentum before collision = total momentum after collision (when no external force acts). This explains recoil of a gun, rocket propulsion, and collision behaviour.
Download: https://ncert.nic.in/textbook/pdf/iesc109.pdf | Complete book: https://ncert.nic.in/textbook/pdf/iesc1ps.zip
Both have the same speed, but the truck has much more mass. Momentum = mass × velocity, so the truck has more momentum. More force or more time is needed to change this larger momentum (F = Δp/Δt). This is why heavy vehicles need larger brakes and longer stopping distances.
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