2.2.1 · D5 · HinglishFluid Mechanics
Question bank — Fluid definition — shear stress, no fixed shape
2.2.1 · D5· Physics › Fluid Mechanics › Fluid definition — shear stress, no fixed shape
Shuru karne se pehle, vocabulary ka ek reminder, taaki koi bhi symbol unexplained na rahe:
Recall Woh chaar words jinka use neeche har sawaal mein hota hai
- Shear stress ::: ek sideways (tangential) force jo ek area par spread hoti hai — woh push jo ek layer ko doosri ke upar slide karane ki koshish karti hai.
- Normal stress ::: ek perpendicular force jo ek area par spread hoti hai — surface ke andar/bahar seedha push ya pull.
- Strain ::: koi cheez kitni zyada tilt/deform hui hai (ek angle).
- Rate of strain ::: woh tilt abhi kitni tezi se badh rahi hai (ek velocity gradient, units ).
Sahi hai ya galat — justify karo
A fluid can never carry any shear stress at all.
Galat. Yeh zero shear sirf rest mein carry karta hai; ek moving fluid carry karta hai, aur yehi cheez honey ko hilaana mushkil banati hai.
Gases fluids nahi hain kyunki woh paani ki tarah pour nahi hote.
Galat. "Fluid" define hota hai kisi bhi shear ke aage jhuk jaane se, aur gases bhi liquids ki tarah flow karti hain aur apna container bhar leti hain — isliye dono fluids hain.
Ek solid bhi shear ke under deform hota hai, toh solid ek tarah ka fluid hai.
Galat. Ek solid ek fixed tilt tak pahunchta hai aur ruk jaata hai (), stress ko ek spring ki tarah store karta hai; ek fluid kabhi tilt karna band nahi karta, isliye dono fundamentally alag hain.
Agar aap bahut chhota shear stress apply karo, toh fluid usse resist karega aur still rahega.
Galat. Definition kehti hai "koi bhi shear, chahe kitna bhi chhota ho" isse flow karaata hai — koi bhi aisi threshold nahi hai jiske neeche ek (Newtonian) fluid ruka rahe.
Rest mein ek fluid mein sirf normal (pressure-like) stresses hoti hain.
Sahi. Static equilibrium mein zero shear ke saath, sirf perpendicular pushes bachti hain — yehi wajah hai ki Hydrostatics — Fluids at Rest sirf pressure se deal karta hai.
"No fixed shape" aur "cannot resist shear" fluid ki do independent properties hain.
Galat. Yeh ek hi fact ke do roop hain: slanted surfaces par shear support se shape hold karna hota hai, jo ek fluid de nahi sakta — toh no-shape, no-shear se naturally aata hai.
Ek Newtonian fluid par shear stress double karne se woh jitna deform hua hai woh double ho jaata hai.
Galat. Fluid ke liye, rate set karta hai, toh double karne se shearing ki speed double hoti hai, accumulated angle nahi — angle to waise bhi badhta rehta hai.
Ek zyada viscous fluid ek static shear stress support kar sakta hai jo ek patla fluid nahi kar sakta.
Galat. Koi bhi Newtonian fluid zero static shear support karta hai; zyada viscosity ka matlab sirf yeh hai ki woh dheere flow karta hai, ruk nahi jaata.
Error dhundo
"Paani table par apni shape rakhta hai jab tak kaafi tez hawa na chale."
Error yeh hai: fluids mein koi shear threshold nahi hoti. Halki hawa bhi deti hai; paani isliye failta hai kyunki static shear ke liye hai, toh usne kabhi sach mein "apni banayi hui" shape "rakhi" hi nahi thi.
", toh shear stress, viscosity ka tilt angle se product hai."
Error yeh hai: yeh hona chahiye — tilt ki rate, na tilt . Woh wala form Stress and Strain in Solids ka hai.
"Kyunki stress force over area hai, same drag force ke liye ek badi plate zyada shear stress feel karegi."
Error yeh hai: fixed force ke liye area ke saath ghatta hai. Bada area same force ko zyada phatlaata hai, toh intensity (stress) kam ho jaati hai.
"Rest mein ek fluid mein kisi bhi tarah ka zero stress hota hai."
Error yeh hai: rest mein sirf shear stress zero hoti hai; normal stress (pressure) bilkul maujood hoti hai — yahi upar fluid ke column ko thaame rakhti hai.
"Velocity gradient ki units velocity hain."
Error yeh hai: yeh velocity per distance hai, — ek inverse time, jis rate se shear angle badhta hai.
"Kyunki gases flow karti hain, unki viscosity liquids se zyada honi chahiye."
Error yeh hai: flow karna viscosity nahi hai. Gases ki actually zyada liquids se bahut kam hoti hai; dono flow karte hain sirf isliye kyunki dono fluids hain.
Why questions
Ek fluid apne container ki shape neeche se upar tak kyun leta hai?
Kyunki yeh slanted surfaces par shear balance nahi kar sakta, yeh gravity ke under collapse ho jaata hai jab tak har surface horizontal na ho jaaye (ya walls se match na kare), pehle niche ke points bhar ke.
Stress define karne ke liye hum force ko area se kyun divide karte hain, sirf force use karne ki jagah?
Deformation push ki intensity par depend karti hai, total force par nahi — same force ek needle par devastating hai lekin ek wall par phailaane se gentle hai.
Newton's law use kyun karta hai na ki solids ki tarah strain ?
Fluid ki tilt kabhi ek fixed par settle nahi hoti, toh stress se relate karne ke liye ek stable quantity nahi hai; rate well-defined hai aur steady flow mein constant hoti hai. Dekho Velocity Profile and No-Slip Condition.
Static equilibrium mein ek fluid sirf normal stress kyun carry karta hai?
Koi bhi bacha hua shear isse deform karta rahega, toh woh rest mein nahi ho sakta jab tak saari shear ne fluid ko ek aisi shape mein na la diya ho jahan shear vanish ho jaaye — sirf perpendicular pushes bachti hain.
Honey ko hilaana paani se zyada mushkil kyun hai jabki dono follow karte hain?
Honey ki viscosity bahut badi hoti hai, toh same banane ke liye tumhe bahut bada supply karna padta hai — dekho Viscosity and Newtonian vs Non-Newtonian Fluids.
Pressure ko "normal stress" kehna fluids ko Pressure in Fluids se kyun connect karta hai?
Pressure wahi normal-stress hai jo ek fluid se push karta hai; kyunki rest mein fluids mein sirf normal stress hoti hai, pressure static fluids ki poori kahaani hai.
Edge cases
Jab velocity gradient exactly zero ho toh shear stress kya hogi?
Zero — layers ke beech koi relative sliding nahi matlab koi shear nahi, jo bilkul kisi bhi fluid ki static-rest condition hai.
Ek fluid film mein dono plates same speed se move kar rahi hain. Kya shear stress hai?
Nahi — poori film ek block ki tarah saath move karti hai, toh aur ; sirf motion shear nahi banata, sirf relative motion banata hai.
Jab viscosity (ek "ideal" fluid), ek given par shear stress ka kya hoga?
: fluid bina kisi resistance ke slide karta hai, ek aisa idealization jahan layers kabhi ek doosre ko grip nahi karti — ek useful limiting model, real substance nahi.
Jab viscosity , kya fluid solid ban jaata hai?
Bilkul nahi — yeh zyada se zyada dheere flow karta hai aur choti timescales par solid jaisa lagta hai, lekin itna time dene par koi bhi Newtonian fluid phir bhi flow karta hai, kyunki woh phir bhi static shear hold nahi kar sakta.
Steel ka ek blob aur paani ka ek blob dono ek halki hawa feel karte hain. Outcome mein key difference kya hai?
Steel ke zariye resist karta hai, imperceptibly tilt hoke apni shape rakha hai; paani mein static shear ke liye hai, toh aur woh fail jaata hai — woh us shape mein kabhi static equilibrium nahi pa sakta.
Jis moment shear pehli baar still paani par apply hoti hai, kya velocity gradient bada hai ya chhota?
Pehle chhota (fluid rest mein tha), lekin yeh turant badhna shuru ho jaata hai kyunki koi bhi , force karta hai — fluid deform hona shuru karta hai aur karta rehta hai, koi settling point nahi.
Connections
- Parent topic (Hinglish)
- Pressure in Fluids — woh normal stress jo rest mein bachti hai.
- Viscosity and Newtonian vs Non-Newtonian Fluids — ka role.
- Hydrostatics — Fluids at Rest — rest mein sirf normal forces kyun.
- Stress and Strain in Solids — contrasting law.
- Velocity Profile and No-Slip Condition — ki origin.