Jab Velocity Badalti Hai ⚡
Jab aap bus mein baithe ho aur driver accelerator dabata hai, aap peeche ki taraf dhakele jaate ho. Jab wo brake maarta hai, aap aage jhukte ho. Dono baar bus ki velocity badal rahi thi. Velocity ke badalne ki dar (rate) ko hi Acceleration (tvaran) kehte hain.
📐 Acceleration (a) = Velocity mein badlaav ÷ Samay
a = (v − u) ÷ t
jahan u = initial velocity, v = final velocity, t = time
SI unit: m/s² (metre per second squared). Ye ek vector hai.
Unit "m/s²" ka matlab samjho: "har second mein velocity kitne m/s badalti hai". Agar a = 4 m/s² hai, toh har second velocity 4 m/s badhti hai - 0, 4, 8, 12, 16... aise.
➕➖ Acceleration Ke Types
1. Positive Acceleration (Velocity badh rahi)
Jab velocity badhti hai. Jaise gaadi ka accelerator dabana, ya patthar ka neeche girna. Yahan a ka value positive hota hai.
2. Negative Acceleration (Retardation / Deceleration)
Jab velocity ghatti hai. Jaise brake lagana, ya upar phenka gaya gend. Yahan a negative aata hai. Ise retardation ya deceleration kehte hain.
3. Zero Acceleration
Jab velocity bilkul nahi badalti (uniform velocity). Jaise highway par cruise control se ek hi speed aur direction mein chalti gaadi. Yahan a = 0.
📌 Uniform acceleration = velocity barabar samay mein barabar maatra se badle
(jaise free fall).
Non-uniform acceleration = velocity ka badlaav alag-alag ho (jaise sheher ki
traffic mein gaadi).
🧮 Solved Examples
✔ Example 1 - Positive acceleration:
Ek car rest (0 m/s) se chalkar 5 second mein 20 m/s ki velocity paa leti hai. Acceleration?
a = (v − u) ÷ t = (20 − 0) ÷ 5 = 4 m/s²
✔ Example 2 - Retardation (negative):
Ek car 20 m/s se chal rahi hai aur brake lagane par 4 second mein ruk jaati hai. Acceleration?
a = (0 − 20) ÷ 4 = −5 m/s²
Matlab: retardation = 5 m/s² (minus sign batata hai ki velocity ghat rahi hai).
✔ Example 3 - Units badalna zaroori hai!
Ek bus ki speed 36 km/h se badhkar 10 second mein 72 km/h ho jaati hai. Acceleration nikalo.
Step 1 - m/s mein badlo:
u = 36 × 5/18 = 10 m/s | v = 72 × 5/18 = 20 m/s
Step 2 - formula:
a = (20 − 10) ÷ 10 = 1 m/s²
✔ Example 4 - Final velocity nikalna:
Ek cycle 2 m/s se chal rahi hai aur 3 m/s² se accelerate karti hai. 4 second baad velocity?
a = (v − u) ÷ t → 3 = (v − 2) ÷ 4 → v − 2 = 12 → v = 14 m/s
🌍 Free Fall - Kudrat Ka Acceleration
Jab koi cheez sirf gravity ki wajah se neeche girti hai, toh uska acceleration hamesha ek hi hota hai:
📌 g = 9.8 m/s² (lagbhag 10 m/s² le sakte hain) - ise acceleration due to gravity kehte hain.
Matlab: girti hui cheez ki velocity har second 9.8 m/s badhti hai - 0, 9.8, 19.6, 29.4 m/s... aur ye object ke vazan par depend nahi karta!
Galileo ne kaha tha ki bhaari aur halki cheez ek saath girti hain. Hawa mein pankh (feather) dheere girta hai kyunki hawa uska rasta rokti hai (air resistance). Lekin agar hawa hata di jaaye (vacuum mein), toh patthar aur pankh bilkul ek saath girenge! Ye experiment chaand par astronauts ne kiya tha - hathoda aur pankh ek saath gire, kyunki wahan hawa hi nahi hai.
🤯 Constant Speed Par Bhi Acceleration?
Ek chaunkane wali baat: acceleration sirf speed badalne se nahi hota - direction badalne se bhi hota hai! Kyunki velocity ek vector hai (magnitude + direction), aur inme se kuch bhi badle toh velocity badal gayi.
📌 Ek gaadi jo 40 km/h ki constant speed par ek mod (turn) le rahi hai, wo accelerated motion mein hai - kyunki uski direction badal rahi hai! Isi wajah se turn par aap side mein dhakele jaate ho.
Yahi baat uniform circular motion ka aadhaar hai, jo hum Lesson 6 mein padhenge.
📊 Ek Nazar Mein
| Sthiti | Acceleration | Example |
|---|---|---|
| Velocity badh rahi | Positive (+) | Accelerator dabana, patthar girna |
| Velocity ghat rahi | Negative (−) / retardation | Brake lagana, upar phenka gend |
| Velocity constant | Zero | Highway par ek hi speed & direction |
| Sirf direction badal rahi | Non-zero! | Mod par gaadi, circular motion |
Acceleration ko live badalkar dekho ki gaadi kaise chalti hai aur graphs kaise bante hain!
Open Simulator →✏️ Khud Try Karo (Practice)
Q. Solve karo (answers neeche):
- Ek train 0 se 30 m/s tak 10 s mein pahunchti hai. Acceleration?
- Ek scooter 15 m/s se 3 s mein ruk jaata hai. Retardation?
- u = 5 m/s, a = 2 m/s², t = 6 s. Final velocity v?
Answers: 1) (30−0)/10 = 3 m/s² 2) (0−15)/3 = −5 m/s² (retardation 5 m/s²) 3) v = u + at = 5 + 2×6 = 17 m/s
🧠 Chalo Test Karein! (Quick Quiz)
Apne aap ko check karo 👇
📌 Aage Kya? (Coming Next)
Ab hum motion ko graphs se samjhenge - distance-time aur velocity-time graphs, aur unke slope aur area ka matlab.