Physics 101: Lecture 23, Pg 1 Physics 101: Lecture 23 Fluids l Today’s lecture will cover Textbook Sections 11.1-11.5 è Density è Pressure è Pascal’s Principle.

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Physics 101: Lecture 23, Pg 1 Physics 101: Lecture 23 Fluids l Today’s lecture will cover Textbook Sections 11.1-11.5 è Density è Pressure è Pascal’s Principle

Physics 101: Lecture 23, Pg 2 l Density = Mass/Volume è  = M/V è SI unit: [kg/m 3 ] l Densities of some common things (kg/m 3 ) è Water 1000 è ice 917(floats on water) è blood 1060(sinks in water) è lead 11,300 è Copper 8890 è Mercury 13,600 è Aluminum 2700 è Wood 550 è air 1.29 è Helium 0.18 Physics 101: Density

Physics 101: Lecture 23, Pg 3 Pressure Pressure that a fluid or gas exerts on a surface: P = F / A SI unit: [N/m 2 = Pa] F: force acting perpendicular to surface A: Area of surface Atmospheric presure: 1.01 10 5 Pa

Physics 101: Lecture 23, Pg 4 Pressure and Depth Barometer: a way to measure atmospheric pressure p 2 = p 1 +  gh p atm =  gh Measure h, determine p atm example--Mercury  = 13,600 kg/m 3 p atm = 1.05 x 10 5 Pa  h = 0.757 m = 757 mm = 29.80” (for 1 atm) h p 2 =p atm p 1 =0

Physics 101: Lecture 23, Pg 5 Concept Question Suppose you have a barometer with mercury and a barometer with water. How does the height h water compare with the height h mercury ? 1. h water is much larger than h mercury 2. h water is a little larger than h mercury 3. h water is a little smaller than h mercury 4. h water is much smaller than h mercury CORRECT water is much less dense than mercury, so the same amount of pressure will move the water farther up the column. h p 2 =p atm p 1 =0

Physics 101: Lecture 23, Pg 6 Concept Question Is it possible to stand on the roof of a five story (50 foot) tall house and drink, using a straw, from a glass on the ground? 1. No 2. Yes Even if a person could completely remove all of the air from the straw, the height to which the outside air pressure moves the water up the straw would not be high enough for the person to drink the water. CORRECT

Physics 101: Lecture 23, Pg 7 Concept Question Evacuate the straw by sucking How high will water rise? no more than h = P a /  g = 10.3m = 33.8 feet no matter how hard you suck! h p a p=0

Physics 101: Lecture 23, Pg 8 Summary Density Pressure P 2 = P 1 +  gh Pascal’s Principle

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