Physics 11 Scale Up Fall 2014 Chapter 13

Procedural Notes Ch. 13 quiz today Quiz on Ch. 14 & 15 Friday 21st Lab on Balistic Pendulum on Nov. 19th

13 Fluids

Chapter 13 By the end of Ch. 13 you are expected to know how to: draw a FBD for bodies immersed in fluids, calculate and compare buoyant forces and hydrostatic pressures, apply Pascal’s Principle, the Archimedes’ Principle, the equation of continuity and the Bernoulli’s equation to find different physics quantities (mass, density, volume, velocity, cross sectional area)

Chapter 13

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.

Pressure in a Liquid Increases with Depth

Buoyant force is due to different pressures at the top and bottom of a submerged object. This leads to: upward net force

Summary of Fluid Motion Continuity equation : A1v1 = A2v2 = constant wide (BIG area) low speed narrow (small area) high speed Bernoulli’s equation : high speed (fast) low pressure low speed (slow) high pressure constant

Kissing Elmos If the fan blows the air between the Elmo balloons at 3m/s, what is the force acting to push the balloons together?

Kissing Elmos If the density of Helium in the balloon is 0.1664 kg/m3 and the density of air is 1.205 kg/m3, and the empty balloon weighs ? what extra weight must be tied to the balloon to stop Elmo from blowing away?

What is the density of the sphere? A sphere completely submerged in water is tethered to the bottom of a pool by a string. The tension in the string is 1/3 the weight of the sphere. What is the density of the sphere? r = 750 kg/m3 13.49

What fraction of the cylinder’s length is in the denser liquid? A light liquid with r1 floats on top of a denser liquid with r2. A uniform cylinder of length L and intermediate density r (r1 < r < r2) floats at the interface as shown. What fraction of the cylinder’s length is in the denser liquid? 1 2 h 15.52

What does the top pressure gauge read? A pipe flowing with oil has two pressures gauges on it. The reading on the lower pressure gauge is shown. What does the top pressure gauge read? P = 110 kPa roil = 900 kg/m3 13.33

Chapter 13 By the end of Ch. 13 you are expected to know how to: draw a FBD for bodies immersed in fluids, calculate the buoyant force, use Pascal’s Principle and the Archimedes’ Principle in equation form, use the equation of continuity and the Bernoulli’s equation, manipulate them to find different physical quantities.

Chapter 13

Homework Questions

Buoyant Forces A glass of water is filled to the very top with water and four ice cubes. When all of the ice cubes melt, what happens to the water level in the glass? The water level rises, so some water spills out. The water level goes down. The water level stays the same, right at the top.

Buoyancy upper brick lower brick both the same You are asked to hold one of these two bricks in the indicated position. Which of the two bricks will be easier for you to hold? 20

Buoyancy Rank the weights of the beakers, including their contents, from largest to smallest. B > C > A (A = B) > C C > A > B C > (A = B) A = B = C 21

The Falkirk Wheel 22

The Falkirk Wheel 23

Buoyancy A B ship A ship B both the same Ships A and B have the same height and the same mass, but they have different cross-sectional profiles. Which ship rides higher in the water (i.e. more height above water line)? ship A ship B both the same A B 24

Buoyancy floats as before floats higher in the water floats lower in the water sinks to the bottom An object floats in water with 3/4 of its volume submerged. The object is now placed in oil with a density half that of water. What happens? 25

Buoyancy move up slightly stay at the same place move down slightly sink to the bottom float to the top An object floats in water with 3/4 of its volume submerged. More water is now poured on top of the water, totally covering the object. When the object is released it will: up to surface 26

Buoyancy move up slightly stay at the same place move down slightly sink to the bottom float to the top An object floats in water with 3/4 of its volume submerged. Oil is now poured on top of the water, totally covering the object. When the object is released it will: up slightly 27

V1>(V2=V3)>V4 P4>(P2=P3)>P1 Liquid flows through this pipe. What you are seeing is an overhead view of the pipe. Rank the flow speeds at points 1-4 from largest to smallest. V1>(V2=V3)>V4 Rank the pressures at points 1-4 from largest to smallest. P4>(P2=P3)>P1 15.21