Kitni Tezi Se? 💨
Pichle lesson mein humne dekha ki object kitna chala. Ab dekhte hain wo kitni tezi se chala - yaani Speed aur Velocity. Ye dono ek jaise lagte hain lekin inme ek bahut zaroori farak hai.
⏱️ Uniform aur Non-Uniform Motion
📌 Uniform motion = object barabar samay mein
barabar doori tay kare.
Non-uniform motion = barabar samay mein alag-alag doori tay kare.
| Time | Uniform motion (distance) | Non-uniform motion (distance) |
|---|---|---|
| 1st second | 10 m | 5 m |
| 2nd second | 10 m | 12 m |
| 3rd second | 10 m | 8 m |
| 4th second | 10 m | 20 m |
Examples: Uniform - ek khaali highway par cruise control se chalti gaadi, ghadi ki sui. Non-uniform - sheher ki traffic mein gaadi (rukti, chalti, tez hoti hai), girta hua patthar.
Rozmarra ki zindagi mein bilkul uniform motion milna mushkil hai - traffic light, speed breaker, mod (turn) - sab speed badal dete hain. Isi liye physics mein hum aksar "average" nikalte hain, jo agla topic hai!
💨 Speed (Chaal)
📐 Speed = Distance ÷ Time
SI unit: metre per second (m/s). Ye ek scalar hai (direction
nahi).
📌 Average Speed = Total distance ÷ Total time (jab speed badalti rehti ho).
🔄 Unit Conversion (Bahut Important!)
📐 km/h se m/s: × 5/18
m/s se km/h: × 18/5
✔ Conversion Examples:
72 km/h = 72 × 5/18 = 20 m/s
90 km/h = 90 × 5/18 = 25 m/s
20 m/s = 20 × 18/5 = 72 km/h
✔ Example 1 - Simple speed:
Ek car 240 km ki doori 4 ghante mein tay karti hai. Speed nikalo.
Speed = 240 ÷ 4 = 60 km/h
✔ Example 2 - Average speed:
Ek ladka pehle 100 m 20 second mein, phir agle 100 m 30 second mein chalta hai. Average speed?
Total distance = 100 + 100 = 200 m
Total time = 20 + 30 = 50 s
Average speed = 200 ÷ 50 = 4 m/s
Dhyan do: Ye 5 aur 3.33 ka simple average (4.17) NAHI hai! Hamesha total distance ÷ total time karo.
🧭 Velocity (Veg)
📐 Velocity = Displacement (visthapan) ÷ Time
SI unit: m/s. Ye ek vector hai (magnitude + direction).
Velocity batati hai ki object kis direction mein kitni tezi se ja raha hai. Isliye velocity zero ya negative bhi ho sakti hai - jab displacement zero ya ulti direction mein ho.
📌 Average velocity = Total displacement ÷ Total time
Aur jab acceleration uniform ho, tab: Average velocity = (u + v) ÷ 2
(u = initial velocity, v = final velocity)
✔ Example 3 - Round trip (velocity vs speed):
Ek aadmi ghar se 3 km door bazaar jaata hai aur wapas aa jaata hai. Poore safar mein 2 ghante lage.
Average speed = total distance ÷ time = (3+3) ÷ 2 = 3 km/h
Average velocity = total displacement ÷ time = 0 ÷ 2 = 0
(kyunki wapas wahin pahuncha!)
✔ Example 4 - Average velocity from u and v:
Ek gaadi ki velocity 10 m/s se badhkar 30 m/s ho jaati hai (uniform acceleration se). Average velocity?
= (u + v) ÷ 2 = (10 + 30) ÷ 2 = 20 m/s
📊 Speed vs Velocity - Comparison
| Baat | Speed | Velocity |
|---|---|---|
| Formula | Distance ÷ Time | Displacement ÷ Time |
| Type | Scalar (sirf magnitude) | Vector (magnitude + direction) |
| Value | Hamesha positive (ya 0) | Positive, negative ya zero |
| Round trip par | Zero nahi hoti | Zero ho jaati hai |
| Unit | m/s | m/s |
Gaadi ka speedometer sirf speed batata hai (jaise 60 km/h) - wo direction nahi batata. Isi liye use "speed-o-meter" kehte hain, "velocity-meter" nahi! Direction jaanne ke liye compass ya GPS chahiye.
Ek athlete 400 m ke gol track par ek poora chakkar 50 second mein pura karta hai.
▸ Average speed = 400 ÷ 50 = 8 m/s
▸ Average velocity = 0 ÷ 50 = 0!
Wo bhaag toh raha tha, lekin uski average velocity zero hai - kyunki wo wahin wapas pahuncha!
✏️ Khud Try Karo (Practice)
Q. Solve karo (answers neeche):
- 108 km/h ko m/s mein badlo.
- Ek bus 150 km 3 ghante mein chalti hai. Speed?
- Velocity 5 m/s se 25 m/s hui (uniform acceleration). Average velocity?
Answers: 1) 108 × 5/18 = 30 m/s 2) 150 ÷ 3 = 50 km/h 3) (5+25)/2 = 15 m/s
🧠 Chalo Test Karein! (Quick Quiz)
Apne aap ko check karo 👇
📌 Aage Kya? (Coming Next)
Jab velocity badalti hai, toh use kya kehte hain? Agle lesson mein Acceleration - iske types aur numericals.