Exam 3 Physics 101 Lecture 16 Fluids Physics

Exam 3 Physics 101: Lecture 16 Fluids Physics 101: Lecture 16, Pg 1

States of Matter l Solid èHold Volume èHold Shape l Liquid Fluids èHold Volume èAdapt Shape l Gas èAdapt Volume èAdapt Shape Physics 101: Lecture 16, Pg 2 15

Qualitative Demonstration of Pressure l Force due to molecules of fluid colliding with container. è Impulse = Dp l Average Pressure = F / A y Physics 101: Lecture 16, Pg 3 18

Atmospheric Pressure l Basically weight of atmosphere! l Air molecules are colliding with you right now! l Pressure = 1 x 105 N/m 2 = 14. 7 lbs/in 2! l Example: Sphere w/ r = 0. 1 m èDemo A = 4 p r 2 =. 125 m 2 F = 12, 000 Newtons (over 2, 500 lbs)! Physics 101: Lecture 16, Pg 4 23

Pascal’s Principle A change in pressure at any point in a confined fluid is transmitted everywhere in the fluid. l Hydraulic Lift l Compare the work done by F 1 with the work done by F 2 A) W 1 > W 2 B) W 1 = W 2 C) W 1 < W 2 l Physics 101: Lecture 16, Pg 5 27

Gravity and Pressure l Two identical “light” containers are filled with water. The first is completely full of water, the second container is filled only ½ way. Compare the pressure each container exerts on the table. 1 A) P 1 > P 2 l Under B) P 1 = P 2 2 C) P 1 < P 2 water P = Patmosphere + r g h Physics 101: Lecture 16, Pg 6 31

Dam question A B Two dams of equal height prevent water from entering the basin. Compare the net force due to the water on the two dams. A) FA > FB B) FA=FB C) FA< FB F = P A, and pressure is rgh. Same pressure, same Area same force even though more water in B! Physics 101: Lecture 16, Pg 7 35

Example: Barometer: a way to measure atmospheric pressure p 1=0 p 2=patm h Physics 101: Lecture 16, Pg 8 37

Example: Water Barometer: p 1=0 p 2=patm h Physics 101: Lecture 16, Pg 9 37

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 Physics 101: Lecture 16, Pg 10 40

Archimedes’ Principle l Determine force of fluid on immersed cube èDraw FBD l. Buoyant force is weight of displaced fluid! Physics 101: Lecture 16, Pg 11 43

Archimedes Example A cube of plastic 4. 0 cm on a side with density = 0. 8 g/cm 3 is floating in the water. When a 9 gram coin is placed on the block, how much sinks below water surface? Fb h Mg mg Physics 101: Lecture 16, Pg 12 48

Summary l Pressure is force exerted by molecules “bouncing” off container P = F/A l Gravity/weight effects pressure èP = P 0 + rgd l Buoyant force is “weight” of displaced fluid. F = r g V Physics 101: Lecture 16, Pg 13