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  Question 10.1:Explain whyThe blood pressure in human Atmospheric pressure at a he sea level, though the height Hydrostatic pressure is a scal Answer The pressure of a liquid is gi  P  = hρ gWhere,  P  = Pressure h = Height of the liquid colu  ρ = Density of the liquidg = Acceleration due to the gIt can be inferred that pressu  pressure in human vessels de height of the blood column i  pressure at the feet is more t Density of air is the maximu height from the surface. At a value at the sea level. Atmos of 6 km from the surface, it When force is applied on a li Hence, hydrostatic pressure quantity.Question 10.2: s is greater at the feet than at the brain ight of about 6 km decreases to nearly half of it f the atmosphere is more than 100 km ar quantity even though pressure is force divide en by the relation: n ravity e is directly proportional to height. Hence, the    pends on the height of the blood column in the more at the feet than it is at the brain. Hence, t an it is at the brain. near the sea level. Density of air decreases wi height of about 6 km, density decreases to near heric pressure is proportional to density. Henc ecreases to nearly half of its value at the sea lev quid, the pressure in the liquid is transmitted in oes not have a fixed direction and it is a scalar value at the d by area. lood ody. The e blood th increase in y half ofits , at a height el. all directions. hysical  Explain whyThe angle of contact of mercury with glass is obtuse, while that of water with glass is acute.Wateron a clean glass surface tends to spread out while mercury on the same surface tends to form drops. (Put differently, water wets glass while mercury does not.)Surface tension of a liquid is independent of the area of the surfaceWater with detergent dissolved in it should have small angles of contact.A drop of liquid under no external forces is always spherical in shape Answer The angle between the tangent to the liquid surface at the point of contact and the surface inside the liquid is called the angle of contact ( θ  ), as shown in the given figure. S  la , S  sa , and S  sl are the respective interfacial tensions between the liquid-air, solid-air, and solid-liquid interfaces. At the line of contact, the surface forces between the three media must be in equilibrium, i.e.,The angle of contact θ  , is obtuse if S  sa < S  la (as in the case of mercury on glass). This angle is acute if S  sl < S  la (as in the case of water on glass).Mercury molecules (which make an obtuse angle with glass) have a strong force of  attraction between themselve tend to form drops. On the other hand, water mo force of attraction between t Hence, they tend to spread oSurface tension is the force a liquid and any other surface. Hence, surface tension is als Water with detergent dissolv small θ  , there is a fast capilla liquid is directly proportiona cos θ  will be large and the ris A liquid tends to acquire the tension. The surface area of external forces, liquid drops Question 10.3:Fill in the blanks using the w Surface tension of liquids ge Viscosity of gases. .. with te (increases / decreases)For solids with elastic modul for fluids it is proportional to For a fluid in a steady flow, t (conservation of mass / Bern For the model of a plane in a for an actual plane (greater / Answer decreases s and a weak force of attraction towardsolids. ecules make acute angles with glass. They have emselves and a strong force of attraction towar t. cting per unit length at the interface between th This force is independent of the area of the liqu independent of the area of the liquid surface.    ed in it has small angles of contact ( θ  ). This is b ry rise of the detergent in the cloth. The capilla to the cosine of the angle of contact ( θ  ). If   θ  is of the detergent water in the cloth will be fast. minimum surface area because of the presence sphere is the minimum for a given volume. He lways take spherical shape. ord(s) from the list appended with each stateme erally . . . with temperatures (increases /decrea perature, whereas viscosity of liquids . . . with us of rigidity, the shearing force is proportional . .. (shear strain / rate of shear strain) he increase in flow speed at a constriction follo oulli’s principle) wind tunnel, turbulence occurs at a ... speed for smaller) ence, they a weak solids.  plane of a id surface. ecause for a y rise of a small, then f surface nce, under no nt:ses) temperature to . . . , while s turbulence  The surface tension of a liqui increases; decreasesMost fluids offer resistance t known as viscosity. Viscosit liquids decreases with tempeShear strain; Rate of shear stWith reference to the elastic  proportional tothe shear stra fluids, the shearing force is p Conservation of mass/Berno For a steady-flowing fluid, a conservation of mass/Bernou Greater For the model of a plane in a does for an actual plane. Thi numbers are associated with Question 10.4:Explain whyTo keep a piece of paper hor When we try to close a wate openings between our finger The size of the needle of a s exerted by a doctor while ad A fluid flowing out of a smal A spinning cricket ball in air Answer  d is inversely proportional to temperature.    o their motion. This is like internal mechanical of gases increases with temperature, while vis ature. ain odulus of rigidity for solids, the shearing forc in. With reference to the elastic modulus of rigi roportional to the rate of shear strain. lli’s principle increase in its flow speed at a constriction foll lli’s principle. wind tunnel, turbulence occurs at a greater spe follows from Bernoulli’s principle and differe he motions of the two planes. zontal, you should blow over, not under, it tap with our fingers, fast jets of water gush thr ringe controls flow rate better than the thumb p inistering an injection l hole in a vessel results in a backward thrust o does not follow a parabolic trajectory riction, osity of is ity for ws the d than it t Reynolds’ ugh the essure the vessel
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