# Chapter 13 Fluids.

## Presentation on theme: "Chapter 13 Fluids."— Presentation transcript:

Chapter 13 Fluids

13 Fluids Slide 13-2

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Reading Quiz The SI unit of pressure is N kg/m2 Pa kg/m3 Slide 13-6

Answer The SI unit of pressure is N kg/m2 Pa kg/m3 Slide 13-7

Reading Quiz Gauge pressure is true pressure. Explain. larger than
smaller than the same as None of the above Answer: B Slide 13-8

Answer Gauge pressure is true pressure. Explain. larger than
smaller than the same as None of the above Answer: B Slide 13-9

Reading Quiz The buoyant force on an object submerged in a liquid depends on the object’s mass. the object’s volume. the density of the liquid. both B and C. Answer: D Slide 13-10

Answer The buoyant force on an object submerged in a liquid depends on
the object’s mass. the object’s volume. the density of the liquid. both B and C. Answer: D Slide 13-11

Density Slide 13-12

Pressure The pressure of the water behind each hole pushes the water out. The SI unit of pressure is 1 pascal = 1 Pa = 1 N/m2. Slide 13-13

Pressure in a Liquid Increases with Depth
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Example Problem In a graduated cylinder, 10 cm of oil (ρ = 0.85 g/cm3) floats on top of 20 cm of water (ρ = 1.00 g/cm3). What is the pressure at a height of 10 cm from the bottom of the cylinder? Slide 13-15

Atmospheric Pressure patmos = 1 atm = 103,000 Pa Slide 13-16

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Example Problem The gas in the cylinder is at a pressure of
pgas = 3.0 x 105 Pa. How high is the column of mercury? 3 Slide 13-18

The Barometer Slide 13-19

Pressure Units Water pressure not only important in pipes for water, but in sleep Apnea measures. Slide 13-20

Buoyancy Slide 13-21

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Floating When the object sinks to the point that the weight of the displaced fluid equals the weight of the object, then the forces balance and the object floats in equilibrium. No net force. The volume of fluid displaced by a floating object of density o and volume Vo is The density of ice is 90% that of water. When ice floats, the displaced water is 90% of the volume of ice. Thus 90% of the ice is below water and 10% is above. Slide 13-23

How a Boat Floats Slide 13-24

Checking Understanding
Two blocks of identical size are submerged in water. One is made of lead (heavy), the other of aluminum (light). Upon which is the buoyant force greater? On the lead block. On the aluminum block. They both experience the same buoyant force. Answer: C. They both displace the same volume of water so the buoyant force on each is the same. Slide 13-25

Answer Two blocks of identical size are submerged in water. One is made of lead (heavy), the other of aluminum (light). Upon which is the buoyant force greater? On the lead block. On the aluminum block. They both experience the same buoyant force. Answer: C. They both displace the same volume of water so the buoyant force on each is the same. Slide 13-26

Checking Understanding
Two blocks are of identical size. One is made of lead, and sits on the bottom of a pond; the other is of wood and floats on top. Upon which is the buoyant force greater? On the lead block. On the wood block. They both experience the same buoyant force. Answer: A. The lead block, which is completely submerged, displaces a greater volume of water than the floating wood block. Slide 13-27

Answer Two blocks are of identical size. One is made of lead, and sits on the bottom of a pond; the other is of wood and floats on top. Upon which is the buoyant force greater? On the lead block. On the wood block. They both experience the same buoyant force. Answer: A. The lead block, which is completely submerged, displaces a greater volume of water than the floating wood block. Slide 13-28

Checking Understanding
A barge filled with ore floats in a canal lock. If the ore is tossed overboard into the lock, the water level in the lock will rise. fall. remain the same. B. Imagine throwing ore with an enormous density overboard. Then they would barely displace any water, so that the water would barely rise due to this effect. But the boat would be much lighter and float much higher in the water, allowing the water in the lock to fall. Slide 13-29

Answer A barge filled with ore floats in a canal lock. If the ore is tossed overboard into the lock, the water level in the lock will rise. fall. remain the same. Answer: B. Imagine throwing ore with an enormous density overboard. Then they would barely displace any water, so that the water would barely rise due to this effect. But the boat would be much lighter and float much higher in the water, allowing the water in the lock to fall. Slide 13-30

Example Problem A block of plastic floats in water. 20% of the block’s volume is above the waterline. What is the density of the block? Slide 13-31

Example Problem A ball weighing 1.0 N has a density 1/3 that of water. What is the tension in the string when the ball is held under water as shown? Slide 13-32

Constrained Flow: Continuity
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Acceleration of Fluids
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Bernoulli’s Equation Slide 13-36

Example Problem In an agricultural irrigation system, water is pumped through a constant-diameter pipe up a 1.5-m-high embankment, where it empties into a field. If the farmer wants to pump water at a rate of 20 L/s, what pressure does his pump need to apply at the bottom of the pipe? Slide 13-37

Viscosity Slide 13-38

Poiseuille’s Equation
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Example Problem A garden hose is 10 m long and has an inner diameter of 2.5 cm. Using this hose it takes 5.0 s to fill a 10 L bucket. What is the water pressure at the spigot end of the hose? Slide 13-40

Summary Slide 13-41

Summary Slide 13-42