pg 390404 Todays Learning Objectives Know the terms in this chapter Be able to solve word problems involving pressure What is the relationship between pressure and depth of fluid Fluid Pressure Sec 131 ID: 628650
Download Presentation The PPT/PDF document "Forces in Fluids PSCI: Chapter 13," is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Forces in Fluids
PSCI: Chapter 13,
pg
390-404Slide2
Today’s Learning Objectives:
Know the terms in this chapter.
Be able to solve word problems involving pressure.
What is the relationship between pressure and depth of fluid?Slide3
Fluid Pressure (Sec 13-1)
Fluid
–
Any
material that
takes the shape of its containerLiquids and gassesAll fluids exert pressurePressure –The result of force distributed over an areaSlide4
Fluid Pressure
Formula for pressure:
Unit
=
Pascal (Pa
)1 Pa = 1 N/m21 kPa
= 1000 PaSlide5
MathBREAK
You can calculate the pressure using this equation:
Find the pressure exerted by a 3,000 N crate with an area of 2 m
2
.
What is the pressure in kPa?Slide6
The MathPractice Problem:
The force of the atmosphere weighing on a person standing next to the ocean would be 182,000 N. If the average person’s surface area is 1.80 m
2
, what is the pressure of the atmosphere at that elevation?
Step
1: (equation) Step 2: (substitute #’s/labels) Step 3: (answer + label)
Answer = 101,111 PaSlide7
Separate Sheet #1Question:
If the air inside a balloon exerts a force of 1.5 N on an area of 0.5 m
2
, what is the pressure inside the balloon
?
Step 1: (equation) Step 2: (substitute #’s/labels) Step 3: (answer + label) Slide8
Fluid PressureFluids exert pressure
Ex. water pressure or atmospheric pressure
Water pressure increases as depth increases
The pressure at one depth is constant
The pressure is exerted equally in all directions
That’s why bubbles are round!What was the example in the book with the lake and the bathtub?Slide9
Fluids & Pressure
Atmospheric
pressure
– The
pressure caused by the weight of the atmosphereAir pressure decreases as altitude increasesLarger than you think – exerts the weight of a pineapple on every square cm of your bodySlide10
Fluid Pressure
Pressure depends on the depth of the fluid (whether gas or liquid)
Water pressure depends on the weight of fluid directly above you, ignores rest of fluid
present
Water is more dense than air, so it exerts a greater pressure than air does
10 m of water exerts almost as much pressure as 10,000 m of atmosphereSlide11
Today’s Learning Objectives:
Know Pascal’s principle and an example of it.
Know Bernoulli’s principle and an example of it.
Be able to draw a diagram of the forces on a wing.Slide12
Forces & Pressure in Fluids (13-2)
What happens when you squeeze a bottle?
Pascal’s principle
– a change in pressure at any point in a fluid is transmitted equally and unchanged in all directions throughout the fluidSlide13
Properties of Fluids
What happens when you squeeze a tube of toothpaste?
Pascal’s principle
– the pressure applied to a fluid is transmitted equally and unchanged throughout the fluid
Ex. Tube of toothpasteSlide14
Fluids flow …
Fluids flow from areas of high pressure to areas of low pressure
That’s how a straw works
That’s how your
lungs
workSlide15
Properties of FluidsHydraulics
– the science of applying Pascal’s principle
Hydraulics can be used to multiply small forces into much larger forces
Hydraulic brake animation
Slide16
The Math
Pascal’s Principle (Equation)
:
Remember this is the principle where forces are transmitted throughout a fluid equally?
Slide17
The Math
Example Problem
:
A
hydraulic lift is used to lift a heavy machine that is pushing down on a 2.8 m
2 platform with a force of 3,700 N. What force must be exerted on a 0.072 m2 piston to lift the heavy machine?
Step 1: (equation) Step 2: (substitute #’s/labels)
Step
3: (answer + label)
Answer = 95.14 NSlide18
Separate Sheet #2
Problem:
A hydraulic system in a scrap yard is set up to lift loads of
12,750
N on a piston with an area
of 3.9 m2. If the maximum force that can be applied to the smaller piston is 475 N, what area must the smaller piston have in order to lift the load?Step 1: (equation)
Step 2: (substitute #’s/labels) Step 3: (answer + label) Slide19
Properties of Fluids
Bernoulli’s Principle
–
As the speed of a moving fluid increases, its pressure decreases
Ex: Hold 2 sheets of paper 5 cm apart and blow between
them2 more demos!Also, somechemical sprayerswork this way.Slide20
Bernoulli’s Principle – Ex. Hose-End SprayerSlide21
Bernoulli’s Principle – Ex. Hose-End SprayerSlide22
Bernoulli’s Principle – Ex. Hose-End SprayerSlide23
Bernoulli’s Principle – Ex. Hose-End SprayerSlide24
Bernoulli’s Principle explains how airplane wings workFaster moving air on top of wing exerts less pressure than slower air on bottom of wing
Causes “lift”
Forces & Pressure in
FluidsSlide25
Forces & Pressure in Fluids
Other factors determining lift on airplane wing:
Thrust
– the forward force produced by engine
Wing size
– need larger wings for slower aircraft (glider) than faster aircraft (jet)Drag – Force that opposes motion in fluid
This is just another term for fluid friction, we’ve studied this beforeDraw an airplane (wing) with all the forces shown Slide26
Today’s Learning Objectives:
What is buoyant force?
Know Archimedes Principle.
Why do some objects float while others sink?Slide27
Buoyancy (13-3)
Buoyant force
–
The upward force that all fluids exert on matter
Pressure increases w/depth, so more pressure on the bottom than top
Net force is upwardSlide28
Buoyancy
Archimedes’ principle
–
The buoyant force on an object
is equal to the weight of the fluid displaced by an object
In other words, the amount of buoyant force depends on the weight of the fluid moved Slide29
Buoyancy
An object will sink if its weight is greater than the buoyant force acting on it
An object
is suspended (ex. floats) when
it displaces a volume of water equal to its
weight (link)Slide30
Properties of FluidsAn object
sinks if
its weight is greater than the buoyant force acting on it
An object
floats when
it displaces a volume of water equal to its weight (link)Slide31
Buoyancy
Considering density:
If greater density than fluid – sink
If less dense than fluid – float
Examples:
Styrofoam in waterHelium balloons in airSlide32
How does a steel ship float?
Steel is far denser than water
But boat built with hollow shape
Overall density of boat, including air inside it, is less than waterSlide33
Buoyancy
Regulating sinking
Submarines can regulate if they sink or float, by adding or removing water from tanks (increasing or decreasing overall density
)
Very cool info: pg 402-403
Most fish do the same thing by adding or removing air from their swim bladder