PhysicsMarichi · UPSC
Parachute, Drag aur Terminal Velocity
Baarish ki boond itni oonchai se girti hai, phir bhi goli jaisi chot kyun nahi karti?
Socho pehle… phir dekho jawab
Kyunki hawa ek fluid hai jo girti cheez pe drag lagati hai. Speed badhti hai to drag bhi badhta hai, aur ek point pe drag = weight ho jata hai. Wahan acceleration zero, speed constant — isey terminal velocity kehte hain.
Hawa mein girti cheez pe do forces hain: neeche weight (mg), upar drag. Drag roughly F = ½ ρ v² Cd A se chalta hai — yaani speed ka square aur area dono matter karte hain. Isliye boond, dhool, patang ki dori sab jaldi apni terminal velocity pe aa jaate hain.
Parachute ka poora game A (area) aur Cd badhane ka hai. Bada canopy khulte hi drag itna badhta hai ki terminal velocity kuch metre per second tak aa jaati hai — utni speed pe zameen chhoona safe hai. Cyclist jab jhuk kar chalata hai to woh ulta kaam kar raha hai: A kam, drag kam.
Space capsule mein ek hi bada parachute tez speed pe kholo to jhatka aur phatne ka risk. Isliye staging hoti hai: pehle chhote drogue parachutes capsule ko stable karke dheema karte hain, phir main parachutes final descent sambhaalte hain. Aur redundancy — ek fail ho to baaki bacha lein. Yeh human-rating ka core engineering principle hai.
Prelims angle: vacuum mein (jaise Moon pe) hathoda aur pankh ek saath girte hain — wahan drag hi nahi, to terminal velocity ka concept bhi nahi. Terminal velocity sirf fluid (hawa, paani, tel) mein hoti hai.
Ghar pe try karo
Do same kaagaz lo. Ek ko gola bana do, doosra khula rakho. Ek hi oonchai se saath chhodo. Mass same hai, phir bhi gola pehle girega — farak sirf area aur drag ka hai.
Wow!
Baarish ki boond ko agar hawa na rokti, to badal ki oonchai se girti boond chot pahuncha sakti thi — drag hi humara invisible chhaata hai.
3 sawaal
- Terminal velocity ke baare mein kaunsa kathan sahi hai?
Jawab dekho
Is par net force zero hota hai aur speed constant rehti hai. Drag weight ke barabar ho jaata hai, net force zero, isliye speed constant. Vacuum mein drag nahi, to terminal velocity bhi nahi.
- Chandrama par ek hathoda aur ek pankh ek saath chhode gaye. Kya hoga?
Jawab dekho
Dono ek saath girenge. Trap: Moon pe hawa nahi, isliye drag nahi. Gravity dono ko same acceleration deti hai, mass se farak nahi padta.
- Space capsule mein pehle chhote drogue parachute kyun khole jaate hain?
Jawab dekho
Tez speed pe capsule ko stable aur dheema karne ke liye, taaki main parachute safe khul sake. Bahut tez speed pe bada canopy kholna jhatka aur phatne ka risk hai; drogue pehle speed kam karke stable karte hain.
NCERT se jodo: GS3 — Science & Technology (space technology, Gaganyaan); NCERT Class 11 Physics — laws of motion aur mechanical properties of fluids (viscosity, terminal velocity)