Video narration
Chalti bus brake lagaye, to sharir aage kyon jhuk jata hai - kya koi force use aage kheench raha hai? Bus aur sharir ek disha mein motion mein the. Bus rukti hai, lekin body turant nahin rukti. Yahin intuition badalti hai: body aage khinch nahin rahi; vah apni previous motion banaye rakhne ki tendency dikha rahi hai. Newton's First Law kahta hai: bina net external force ke, rest mein object rest mein rahti hai, aur motion mein object usi disha mein uniform motion, constant speed se, banaye rakhti hai. Bus ki speed badalti hai, lekin body ko rokne wala force seat, floor aur friction se turant nahin milta; isliye body aage move karti hai. Inertia koi force nahin hai; yah motion mein badlav ka resistance, yani tendency hai. To jawab hai: bus brake lagte hi hum aage jhukte hain, kyonki body previous motion banaye rakhti hai. Isi tendency ko inertia kahte hain.