Define free fall
Scenario
Agar aap ek stone aur ek feather ko vacuum mein ek saath chhod do, toh dono ek saath zameen par girenge.
Free fall kya hota hai, aur isme 'free' ka kya matlab hai?
Mental model
Free fall matlab sirf aur sirf gravity ki sunna.
Jab koi cheez neeche gir rahi hoti hai aur uspar sivaye earth ki gravity ke, koi aur force (jaise air resistance, engine thrust) nahi lag raha hota, tab hum kehte hain ki woh object free fall mein hai.
Explanation
Normally jab koi object zameen ki taraf girta hai, toh do forces kaam karte hain: earth ki gravity usse neeche kheenchti hai, aur hawa (air resistance) uski speed rokne ki koshish karti hai.
Lekin physics mein 'free fall' ek special condition hai. Agar hum hawa ko gayab kar dein (vacuum mein) aur object ko chhod dein, toh uspar lagne wala akela force sirf earth ki gravitational force hoga.
Jab koi body exclusively gravitational force ke influence mein fall karti hai, uss state ko 'free fall' kehte hain. Is state mein object ki direction change nahi hoti, woh seedha neeche aata hai, lekin uski raftaar lagataar badhti rehti hai.
Real life mein pura free fall thoda mushkil hai kyunki hawa humesha hoti hai, par heavy objects (jaise pathar) ke girne ko hum free fall maan lete hain kyunki unpar air resistance ka asar bahut thoda hota hai.
Worked example
Problem: A parachutist is falling towards the earth with his parachute open. Is he in a state of free fall?
- Hamein dekhna hai ki kaun kaun se forces lag rahe hain. Gravity neeche kheench rahi hai.
- Lekin khula hua parachute bahut zyada air resistance create kar raha hai, jo object ko rok raha hai. Iska matlab force of gravity akeli nahi hai.
Answer: No, because the parachutist is experiencing significant air resistance, so it is not exclusively under the influence of gravity.
Problem: An object is dropped on the Moon, where there is no atmosphere. Is it considered free fall?
- Moon par koi hawa (atmosphere) nahi hai, isliye air friction zero hai.
- Object par sirf Moon ki gravity kaam kar rahi hai, isliye yeh purely free fall ka case hai.
Answer: Yes, because only the Moon's gravitational force is acting on it.
Key points
- Only Gravity: Free fall occurs only when the object is moving exclusively under the influence of gravitational force.
- No Air Resistance: Ideal free fall can only be observed in a complete vacuum.
Common mistakes
- Confusing zero gravity with free fall: Astronauts space station mein 'weightless' feel karte hain, woh isliye kyunki space station aur astronaut dono ek constant free fall mein earth ke around ghoom rahe hote hain, zero gravity nahi hoti.
Recall questions
- What is the only force acting on a body during true free fall?
- What is free fall?
- Is acceleration constant during free fall near the earth's surface?
Questions & answers
What do you mean by free fall?
Whenever objects fall towards the earth under the influence of gravitational force alone, we say that the objects are in free fall.
Approach: Emphasize the word 'alone' or 'only' when mentioning gravitational force.
Does a heavier object fall faster than a lighter object in a vacuum?
No, they fall at the same rate.
Approach: Acceleration due to gravity is independent of the object's mass.
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