1.2.1 · D5 · HinglishNewton's Laws & Dynamics
Question bank — Newton's first law — inertia, operational definition of force
1.2.1 · D5· Physics › Newton's Laws & Dynamics › Newton's first law — inertia, operational definition of forc
Traps se pehle yeh pictures zaroor dekhlo
Neeche ke answers mein teen ideas baar baar aate hain. Inhe ek baar visually samjh lo, aur traps asaan ho jayenge.
Figure dekho: magenta arrow ek object hai; uska orange shadow (across) aur violet shadow (up) uske do components hain. Constant velocity ka matlab hai poora arrow — length AUR direction — kabhi nahi badlta. Koi bhi ek badal do aur arrow alag ho jaata hai, yahi har circular-motion trap ki jad hai.
Upar ka free-body diagram book dikhata hai: gravity (violet, neeche) aur table ka normal push (orange, upar) equal-length arrows hain jo opposite direction mein point karte hain. Woh cancel hokar ek zero net arrow banaate hain — toh book ek free body hai rest mein, bilkul first law ka balanced case.
Sach ya jhooth — justify karo
Zero net force wali body rest mein honi chahiye.
Jhooth. Zero net force ka matlab constant velocity hai, aur constant velocity mein koi bhi steady straight-line speed shaamil hai — rest toh bas special case hai .
Agar koi object move kar raha hai, toh koi force use push kar rahi hogi.
Jhooth. Yeh Aristotle ki galti hai. Ek baar move karne ke baad, object kisi net force ke bina chalte rehta hai; force sirf motion ko change karne ke liye chahiye, use sustain karne ke liye nahi.
Constant speed par move karne wale object par hamesha zero net force hoti hai.
Jhooth. "Constant speed" aur "constant velocity" alag cheezein hain — fixed speed par circle karte body ka direction har moment badalta hai (inward change-arrow figure dekho), toh uski velocity badlti hai aur ek net (centripetal) force lagti hai. Dekho Uniform circular motion.
First law sirf ka special case hai jab ho.
Jhooth. Yeh do extra kaam karta hai: yeh force ko operationally define karta hai (velocity change ke cause ke roop mein) aur yeh assert karta hai ki inertial frames exist karte hain — dono mein se koi bhi akele Newton's second law — F=ma se nahi aata.
Bhaari objects mein zyada inertia hoti hai.
Sach. Inertia ko mass se measure kiya jaata hai, toh zyada mass matlab motion mein kisi bhi change ke liye zyada resistance — shuru karna, rokna, ya morna, sab mushkil.
Inertia ek force hai jo cheezein move karti rehti hai.
Jhooth. Inertia bilkul bhi force nahi hai; yeh ek property hai (motion mein change ke liye resistance). Koi push exert nahi hoti — object bas khud apne aap chalte rehta hai.
Brake lagate bus mein ek real forward force passenger ko aage phenk deti hai.
Jhooth. Torso par koi forward force nahi lagti; woh bas inertia ki wajah se purani speed par chalte rehta hai jabki bus uske neeche decelerate hoti hai. Yeh "dhakka" ek illusion hai.
First law har reference frame mein valid hai.
Jhooth. Yeh sirf inertial frames mein valid hai. Accelerating frame mein ek free body bina kisi real force ke accelerate hoti dikhai deti hai, toh law wahan kaam nahi karta — dekho Inertial vs non-inertial frames.
Ek frame inertial hai agar aur sirf agar usmein ek free body constant velocity se move kare.
Sach. Yahi woh operational test hai jo first law provide karta hai; jis frame mein free bodies drift ya curve karein woh non-inertial hain.
Galti dhundo
"Dishes isiliye rukti hain kyunki tez chalti cloth unpar koi friction exert nahi karti."
Galat reason. Friction zaroor lagta hai, lekin sirf us chhoti si time ke liye jab cloth unke neeche hoti hai, toh impulse (total nudge) aur isliye velocity change negligible hoti hai — baaki kaam unki inertia karti hai.
"Cruising plane par zero net force hai, isliye uske engines band hain."
Galat conclusion. Kaafi saari forces kaam karti hain; woh cancel karti hain. Thrust drag ko balance karta hai aur lift weight ko, engines full speed par chalte hue bhi zero net force deta hai.
"Circle mein constant speed follow karti hai kyunki speed nahi badlti."
Galti: first law demand karta hai ki poora velocity vector (length aur direction) constant rahe. Direction har instant badlti hai, toh velocity badlti hai aur ek net inward force zaroori hai.
"Carousel par mujhe bahar phenka jaata feel hota hai, toh ek outward force real hai."
Outward feeling ek pseudo-force hai, jo rotating (non-inertial) frame mein motion describe karne ka ek artifact hai. Ground (inertial) frame mein sirf real force andar ki taraf hai. Dekho Pseudo-forces.
"Mass aur weight ek hi cheez hain, toh zyada inertia ka matlab Earth aur Moon dono par gravity se zyada force hai."
Mass (inertia ka measure) har jagah fixed rehta hai; weight ek force hai jo local gravity par depend karta hai aur Earth aur Moon ke beech badal jaata hai — dekho Mass vs weight.
"Ek book table par ruk jaati hai, jo prove karta hai motion ke liye continuous force chahiye."
Book isiliye rukti hai kyunki ek hidden force, friction, kaam karti hai. Ise hata do (ice, air-track, space) aur book kabhi nahi rukti, jo exactly wahi hai jo first law predict karta hai.
Why waale sawaal
Law straight line par kyun insist karta hai na ki sirf constant speed par?
Kyunki velocity ek vector hai (direction wala arrow): arrow ki length same rakhte hue use morna phir bhi velocity change karta hai, jiske liye net force chahiye — sirf fixed speed par straight-line motion truly force-free hoti hai.
First law ko force ki operational definition kyun kaha jaata hai?
Yeh ek aisa test deta hai jo tum perform kar sakte ho: ek free particle ko dekho; uski velocity mein koi bhi change reveal karta hai ki ek force kaam ki. Force ko uske symptom (acceleration) se detect kiya jaata hai, directly nahi dekha jaata.
Second law humein kyun nahi bata sakta ki kaunse frames valid hain?
yeh maanta hai ki tumhe pehle se real forces aur ek accha frame pata hai. First law woh foundation provide karta hai yeh declare karke ki kaunse frames (inertial wale) second law ko apply karne ke liye honest hain.
Hum "inertia is equal to mass" ki bajaye "inertia is measured by mass" kyun kehte hain?
Inertia ek qualitative property hai (change ke against stubbornness); mass ek quantitative number hai jo capture karta hai ki ek body mein kitni stubbornness hai.
Friction hatana Newton ko Aristotle se kyun bachata hai?
Aristotle ne "no net force" aur "no force at all" mein confusion ki. Friction woh hidden decelerating force thi; use delete karo aur motion forever chalti rehti hai, jo dikhata hai ki force motion ko change karta hai na ki use maintain karta hai. Dekho Friction.
Edge cases
Agar kisi body par ek instant ke liye net force zero ho, toh kya woh uniform motion mein hai?
Zaroor nahi. Uniform motion ke liye ek interval mein chahiye; ek single instant mein zero net force (jaise, vertical toss ke top par, jahan upward-then-downward force momentarily transition karta hai) just before aur after acceleration allow karta hai, toh velocity constant nahi rehni chahiye.
Kya kisi body ki velocity zero aur net force nonzero ho sakti hai?
Haan. Jis instant tossed ball apne peak par pahunchti hai, lekin gravity phir bhi kaam karti hai, toh — momentary rest woh force-free state nahi hai jo first law describe karta hai.
Kya Earth ki surface ek perfect inertial frame hai?
Nahi, sirf approximately. Earth rotate aur orbit karti hai, toh woh accelerate karti hai; chhote pseudo-forces (jaise Coriolis effect) appear karte hain. Zyaatar bench experiments ke liye deviation negligible hai, toh hum ise inertial treat karte hain. Dekho Inertial vs non-inertial frames.
Ek spacecraft deep space mein engines band karke drift kar raha hai — first law ki kaunsi state mein hai?
Uniform-motion state mein: ke saath woh indefinitely ek straight line mein constant velocity se coast karta hai, inertia ka sabse saaf real example.
Kya rest mein rakhe object par koi forces nahi lagtiñ?
Zaroor nahi — uska koi net force nahi hota. Table par rakhi book par gravity neeche aur normal force upar lagti hai, jo cancel hoti hain (free-body diagram dekho); rest ka matlab hai forces balance hain, na ki woh absent hain.
Connections
- Newton's second law — F=ma — is law mein sirf naam li gayi force ko quantify karta hai.
- Newton's third law — action-reaction — pushes ke peeche force pairs.
- Inertial vs non-inertial frames — jahan first law rehne ki permission hai.
- Friction — woh hidden force jisne Aristotle ko bewakoof banaya.
- Uniform circular motion — constant speed jo phir bhi force maangti hai.
- Pseudo-forces — non-inertial frames ke fictions.
- Mass vs weight — inertia versus gravitational force.