Force Ko "Naapne" Wala Niyam 📐
Pehla niyam batata hai ki force kya karti hai (gati badalti hai). Doosra niyam batata hai ki kitni force lagegi - yaani force ko ek exact formula deta hai. Yahi poore physics ka sabse zyada use hone wala equation hai.
📌 Newton's Second Law: Kisi object par lagne wali force uske momentum ke badalne ki dar (rate of change of momentum) ke barabar hoti hai, aur wo force ki direction mein hoti hai.
Is definition se hi famous formula nikalta hai:
📐 Force = mass × acceleration
F = m × a
SI unit: Newton (N). 1 Newton = 1 kg·m/s²
🔍 F = ma Ki Derivation
Force = momentum ke change ki dar. Chaliye ise formula mein badlein:
Maano object ka mass m hai, initial velocity u, aur t time mein velocity v ho gayi.
Initial momentum = mu, Final momentum = mv
Change in momentum = mv − mu = m(v − u)
Force = change in momentum ÷ time = m(v − u) ÷ t
Lekin (v − u) ÷ t = acceleration (a)! (pichhla chapter)
Isliye: F = m × a ✔
📌 1 Newton kya hai? Wo force jo 1 kg ke object mein 1 m/s² ka acceleration paida kare. Yaani 1 N = 1 kg × 1 m/s² = 1 kg·m/s².
💡 F = ma Se 3 Baatein Samjho
- Zyada force = zyada acceleration: gaadi ka accelerator zyada dabao, wo tez accelerate karegi.
- Zyada mass = kam acceleration (same force par): khaali cycle tez badhti hai, par dher saara saamaan laadi cycle dheere - utni hi taaqat lagane par.
- Formula ko rearrange karke hum a = F/m ya m = F/a bhi nikaal sakte hain.
🧮 Solved Numericals (Step-by-Step)
✔ Example 1 - Basic force:
Ek 10 kg ki cheez ko 5 m/s² se accelerate karna hai. Kitni force chahiye?
F = ma = 10 × 5 = 50 N
✔ Example 2 - Acceleration nikalna:
Ek 20 kg ki cheez par 100 N ki force lagti hai. Acceleration?
a = F ÷ m = 100 ÷ 20 = 5 m/s²
✔ Example 3 - Mass nikalna:
Ek object par 60 N force lagne se 3 m/s² acceleration aata hai. Mass?
m = F ÷ a = 60 ÷ 3 = 20 kg
✔ Example 4 - Pehle acceleration, phir force:
Ek 1000 kg ki car rest se chalkar 5 second mein 20 m/s ki velocity paati hai. Force nikalo.
Step 1 - acceleration: a = (v − u) ÷ t = (20 − 0) ÷ 5 = 4 m/s²
Step 2 - force: F = ma = 1000 × 4 = 4000 N
✔ Example 5 - Brake (force to stop):
Ek 1200 kg ki car 20 m/s se chal rahi hai aur 5 second mein rukti hai. Kitni braking force lagi?
Step 1: a = (0 − 20) ÷ 5 = −4 m/s²
Step 2: F = ma = 1200 × (−4) = −4800 N
Minus sign matlab force motion ke ulti direction mein (braking) thi. Magnitude = 4800 N.
Mass aur force ki sliders badlo aur dekho object kaise accelerate karta hai (F = ma) - live!
Open Lab →⚖️ Weight - Ek Special Force
Newton ke doosre niyam ka ek khaas istemaal: Weight (bhaar). Weight wo force hai jisse prithvi hume apni taraf (neeche) kheenchti hai.
📐 Weight (W) = mass (m) × g
jahan g = acceleration due to gravity = 9.8 m/s² (ya 10 m/s²)
Weight ki unit Newton (N) hai (force hai!), mass ki unit kg.
✔ Example - Mass vs Weight:
Ek ladke ka mass 50 kg hai. Uska weight kitna hai? (g = 10 m/s²)
W = m × g = 50 × 10 = 500 N
Aapka mass har jagah same rehta hai (50 kg toh 50 kg), lekin weight badalta hai! Chaand par gravity (g) prithvi ka sirf 1/6 hai, isliye wahan aapka weight bhi 1/6 ho jaata hai - aap aasaani se uchhal sakte ho! Isi liye astronauts chaand par kood-kood kar chalte hain. Mass = kitna "matter", Weight = gravity kitna kheench rahi hai.
✏️ Khud Try Karo (Practice)
Q. Solve karo (answers neeche):
- Ek 8 kg ki cheez ko 3 m/s² se accelerate karne ke liye force?
- 50 N force ek 10 kg ki cheez par. Acceleration?
- Ek 60 kg ki ladki ka weight? (g = 10 m/s²)
Answers: 1) F = 8×3 = 24 N 2) a = 50÷10 = 5 m/s² 3) W = 60×10 = 600 N
🧠 Chalo Test Karein! (Quick Quiz)
Apne aap ko check karo 👇
📌 Aage Kya? (Coming Next)
Newton ka teesra niyam sabse mazedaar hai - "har action ka barabar aur ulta reaction (abhikriya)" - jisse rocket udta hai aur aap chal paate ho! Agle lesson mein.