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# LPH 105 W15 10:intro

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## Richard Datwyler

on 14 June 2016

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#### Transcript of LPH 105 W15 10:intro

Fluids
Chapter 10 Fluids
Intro.
Pascal
Archimedes
Bernoulli
Flow rate
Phases

Buoyancy
Gauges
Pressure
Density
barometers
Equation
Phases of matter
Gas
Liquid
Solid
compressible
Fills the container
Holds shape well

Not compressible
Fits shape of container.
Chapter 2-9
Fluids
Density
Density is an intrinsic property of a substance.
All similar substances have similar density.

Density is the measure of mass in a given volume
We use this a lot, especially
Which would have more
mass a solid piece of
copper or a solid piece of gold
A. Copper
B. Gold
C. Depends on volume of each
Units
Specific Gravity
no units
Pressure
This is the amount of force over a given area.
Units
Pascal's principle deals with
compression:
If I squeeze a balloon, the pressure
goes up,
not just where I squeeze it, but every
in a confined fluid.
Pascal's Principle
Written as:
A small mass on the smaller area, can lift a larger mass on the larger area.
Barometers work by Pascal's principle. It is also how we get 'mm mercury'.
Buoyancy
Things to note.
The buoyant force is different for each liquid you are in
It is equal to the weight of the displaced fluid
If an object is floating in the fluid, the weight of the displaced fluid is equal to the weight of the object.
Depth doesn't matter.
Show on board
Buoyancy teaches us that if all the ice
in the North pole glacier melted the ocean
would:
A. Rise and destroy coastal regions
B. Fall and create more beach front
C. Stay the same
2 key points (relating the object and the fluid)
Buoyancy and density are used together, often
If the object is floating, the masses are the same.
If the object is submerged the volumes are the same
Fluids in motion
Because we can't destroy or create mass there is an equation of continuity. Meaning the mass, or flow, is continuous.

In general if the fluid is allowed to have a changing density then we need to consider density, otherwise, the continuity equation is described by the
flow rate
equation.
As the fluid moves through the larger area it moves slower, as it hits a narrower area it speeds up.
If the flow rate in one section of
pipe is 15 m^3 / s, and then this pipe narrows
to a cross sectional area of 1.5 m^2. What is the
velocity of the fluid in this section?
A. 10 m/s
B. 15 m/s
C. 1.0 m/s
D. 0.1 m/s
E. 1.5 m/s
Consider driving a car down a high way.
Coming at you head on is a semi truck.
It passes you on your left, but a bit closer
than you might have liked.
What do you notice as you are passed by the truck?

Bernoulli
This is an example of Bernoulli's principle
Where velocity of a fluid is high, pressure is low
Where velocity of fluid is low, pressure is high
Bernoulli derived an equation that helps to
quantify his statement.
It is derived from a work, energy conservation
Thus there is a conserved quantity.
Demo
Applications of Bernoulli principle

ping pong ball
Car and truck
air plane wing
curve ball
etc.

Bernoulli's principle is responsible for all the following except:
A. Air planes lift
B. Smoke rising in chimneys
C. A curve ball
D. Mercury in a barometer

Example 12
The maximum gauge pressure in hydraulic lift is 17.0 atm. What is the largest size vehicle (kg) it can lift if the diameter of the output line is 28.0 cm?

Example 29
An undersea research chamber is spherical with an external diameter of 5.20 m. the mass of the chamber when occupied is 74,400 kg. It is anchored to the sea bottom by a cable. What is (a) the buoyant force on the chamber, and (b) the tension in the cable?
Example 41
A 6.0 cm diameter horizontal pipe gradually narrows to 4.0 cm. When water flows through this pipe at a certain rate, the gauge pressure in these two sections is 32.0 kPa and 24.0 kPa, respectively. What is the volume rate of flow?

Gauge pressure
In my flat bicycle tire, what is the pressure?
Is it zero? (thus a vacuum)
Gauge pressure, is shifted by 1 atm
"To clarify, Archimedes' principle relates to buoyancy, Bernoulli's principle relates to water hoses, and Pascal's principle relates to hydraulics, correct?"
"Does Buoyancy increase as an object is submerged deeper in liquid? "
"Can you explain viscosity? "
"What's the main difference between density and viscosity? I would think that the more density something is the more viscosity it will have too.

I'm not quite seeing how the mass of a displaced fluid is equal to the force of buoyancy."
"I don't really understand the concept of buoyancy."
"Can you explain or give me a better example of Bernoulli's principles "
Full transcript