Define velocity
Scenario
Aap highway par `80 km/h` se car chala rahe ho aur map bata raha hai ki 'keep straight on the highway for `20 km`'.
Speed aur direction ko jab mila dete hain, toh physics mein is combined information ko kya kehte hain?
Mental model
Velocity = Speed with a compass. Yeh batati hai kitni tez aur kis taraf.
Speed sirf ye batati hai ki aap kitna fast ja rahe ho. Lekin Velocity mein speed ke sath direction juri hoti hai. Agar direction thodi bhi change hui (jaise steering wheel ghuma diya), toh velocity change ho jayegi, bhale hi speedometer ki reading same rahe.
Explanation
Physics mein ek point aakar speed thodi adhuri lagne lagti hai. Agar koi aapse kahe ki 'ek gaadi `50 km/h` se bhag rahi hai, use roko', toh aap puchoge 'par kis taraf?'. Yahi kami velocity poori karti hai. Velocity basically kisi object ki speed hai ek specific disha (direction) mein.
Formally define karein toh, velocity is the rate of change of displacement (distance nahi, displacement). Iska formula hota hai: `Velocity = Displacement / Time`. Kyunki displacement ek vector quantity hai jisme direction hoti hai, isliye velocity bhi ek vector quantity hoti hai. Iski value (magnitude) positive, negative, ya zero kuch bhi ho sakti hai depending on the displacement.
Ek interesting situation socho jahan object ek circular track par constant speed par chal raha hai. Yahan speedometer hamesha jaise `20 km/h` dikha raha hai. Toh speed constant hai. Lekin har ek second uski direction badal rahi hai (steering muud raha hai). Kyunki direction badal rahi hai, isliye hum kehte hain ki uski velocity continuously change ho rahi hai.
Velocity ki unit speed ke jaisi hi hoti hai, yani meter per second (`m/s`). Jab hum equations of motion solve karte hain, toh humesha speed ki jagah velocity terms (`u` aur `v`) ka use karte hain, kyunki physics real world ka hisab rakhti hai, jisme direction bohot zaroori hoti hai.
Worked example
Problem: A person walks `100 m` directly North in `20 s`. Calculate his velocity.
- Pehle displacement dekhein, jo direction ke sath hoga.
- Velocity ka formula lagayein (`Displacement / Time`).
Answer: `5 m/s` North
Problem: A toy car returns to its starting point covering a total distance of `20 m` in `5 s`. What is its velocity?
- Starting aur ending point same hain, isliye displacement zero hai.
- Velocity displacement par depend karti hai.
Answer: `0 m/s`
Key points
- Speed with direction: Velocity is the speed of an object moving in a definite direction.
- Vector Quantity: It is a vector quantity. It requires both magnitude and direction.
- Formula: `Velocity = Displacement / Time`.
Common mistakes
- Assuming constant speed means constant velocity: Agar koi `50 km/h` se circle mein ghoom raha hai, to speed constant hai, par disha (direction) lagatar badal rahi hai. Isliye uski velocity 'variable' hogi, constant nahi.
- Not including direction in the answer: Velocity ka final answer dete waqt (khas kar subject questions mein), disha (North, East, right, positive/negative) likhna zaroori hota hai.
Recall questions
- What is the formula for velocity?
- Is velocity a scalar or a vector quantity?
- What happens to velocity if the speed remains constant but the direction changes?
Questions & answers
Under what condition(s) is the magnitude of average velocity of an object equal to its average speed?
When the object moves in a straight line without changing its direction.
Approach: Average velocity uses displacement, while average speed uses distance. Distance and displacement are equal only for straight-line motion in one direction.
Can an object have a constant speed but a variable velocity?
Yes, for example in uniform circular motion, speed is constant but velocity changes due to continuous change in direction.
Approach: Explain that velocity includes direction. If direction changes, velocity changes even if the numerical speed is constant.
Continue learning
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Next: Calculate average velocity
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