PhysicsHiranyagarbha · Class 11-12
Parachute ka jugaad: terminal velocity
Baarish ki boond kaafi upar se girti hai, phir bhi tumhe goli ki tarah kyun nahi lagti?
Socho pehle… phir dekho jawab
Kyunki girte hi hawa peeche kheenchti hai (drag). Speed badhti hai toh drag bhi badhta hai, aur ek point par drag gravity ke barabar ho jaata hai. Us ke baad acceleration zero — boond ek fixed speed par girti hai. Isi ko terminal velocity kehte hain.
Tez speed par hawa ka drag roughly F = ½ ρ C A v² hota hai: ρ hawa ki density, A saamne ka area, C shape factor, aur v speed. Dhyaan do — v ka square. Speed double, drag chaar guna.
Terminal speed par mg = ½ ρ C A v², toh v = √(2mg / ρCA). Matlab area A badhao, toh terminal speed ghategi. Parachute yahi karta hai: chhoti si body ko bahut bada A de deta hai. Chhoti boond ya dhool ke liye viscosity wala Stokes ka niyam (F = 6πηrv) zyada sahi baithta hai — NCERT mein yahi padhoge.
Trade-off yeh hai: bahut tez speed par ekdum bada parachute khule toh jhatka (opening shock) itna hota hai ki kapda ya rassi toot sakti hai. Isliye space capsules pehle chhote 'drogue' parachute kholte hain jo speed kam karte hain aur capsule ko stable rakhte hain, phir bade main parachute. Engineering = physics + safety margin.
Ghar pe try karo
Do ek jaise kagaz lo. Ek ko seedha rakho, doosre ko goli bana do. Dono ko ek saath ek hi oonchai se chhodo. Phir ek plastic thaili ke chaaron kono par dhaaga baandh kar chhota sa parachute banao aur ek rubber ya sikka latkao — area badalne se girne ka time kaise badalta hai, note karo.
Wow!
Skydiver haath-pair phaila kar girta hai toh dheema, aur sar ke bal seedha gota lagaye toh kaafi tez — mass wahi, sirf area badla.
3 sawaal
- Terminal velocity par girti cheez ka acceleration kitna hota hai?
Jawab dekho
Zero. Drag aur weight barabar ho jaate hain, net force zero, toh acceleration zero.
- Drag F ∝ v² ho, aur speed teen guna ho jaaye, toh drag kitna guna?
Jawab dekho
9 guna. 3 ka square 9 hota hai.
- Capsules pehle chhote drogue parachute kyun kholte hain?
Jawab dekho
Tez speed par seedha bada parachute khulne ka jhatka bahut zyada hota. Drogue speed kam aur capsule stable karta hai, phir main parachute safely khulta hai.
NCERT se jodo: NCERT Class 11 Physics — mechanical properties of fluids (viscosity, Stokes ka niyam, terminal velocity) aur laws of motion