Video narration
Kis kon par jhuki mez par rakha aapka phone achanak phisalne lagega? Yahi sawaal block par bhi lagu hota hai. Mez ko dheere dheere jhukaiye: kam kon par phone sthir rehta hai, kyunki gharshan use neeche khiskne se rokta hai. Block par teen bal hain. Bhaari seedha neeche, normal force satah ke lambavat, aur static friction dhalan ke saath upar, sambhavit neeche ki gati ke ulat. Static friction shuru se adhiktam nahin hota; vah zaroorat ke anusaar badhta hai. Ab kon badhaiye. Krantik kon se neeche block ruka rehta hai. Us kon par vah bas chalne wala hai. Yahi angle of repose hai: static friction apni seema tak pahunchta hai. Kon isse upar jaaye, to maangi gayi gharshan-shakti seema paar kar deti hai, aur block neeche sarkta hai. Is kshan, maanak model mein, tan theta = mus. To phone kis kon par phislega? Usi kon par jahan static friction adhiktam ho jaata hai, yaani angle of repose.