ICP Chapter 8 Liquids amp Gases Have the ability to flow Flow the pieces can move around each other Because they can flow they are called fluids Density Density a measure of compactness or ID: 536760
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Slide1
Fluid Mechanics
ICP
Chapter 8Slide2
Liquids & Gases
Have the ability to flow.
Flow = the pieces can move around each other.
Because they can flow, they are called
fluids
.Slide3
Density
Density
a measure of compactness, or
how much mass occupies a given space, or
amount of matter per unit volumeSlide4
Density (cont.)
Units = g/cm
3
or kg/
mL
water = 1 g/cm
3Mercury = 13.6 g/cm3Iridium = 22.6 g/cm3
(densest substance on Earth)Slide5
Density Problem
A block has a mass of 22 kg. Its volume is 2.6 cm
3
. Calculate its density.Slide6
Concept Checks
Which has greater density,
1 kg of water or 10 kg or water?
Which has greater density,
an entire candy bar or half a candy bar?Slide7
Densities: water = 1.0 g/cm
3
aluminum = 2.7 g/cm
3
ethanol = 0.81 g/cm
3
Looking at the densities above, what do you think will happen when aluminum is placed in water?It sinks because it has a higher densityWhat will happen when ethanol is placed in water?It floats because it has a lower density
What can you predict about the density of ice?
It must be less than water, and it is – 0.92g/cm
3Slide8
8.2 Pressure
in Fluids
Pressure
depends on
force
and
area
.
If you spread the force over
more area
, there is
less pressure
.Slide9
8.2 Pressure
in Fluids
Pressure
depends on
force
and
area
.
If you spread the force over
more area
, there is
less pressure
.
The formula to calculate pressure is
:
Pressure =
force
area
The S.I. unit that we use for pressure is the
pascal
(Pa) Slide10
20 N Push
Which creates more pressure?
20 N Push
10 cm
10 cm
5 cm
5 cmSlide11
If this woman were to step on you, which part of the shoe creates more pressure?
Force
(weight)
Area
Same force over smaller area creates more pressure under the heel.
Force
(weight)Slide12
What causes fluid pressure?
Pressure in fluids is caused by the
particles pushing against a surface
.
Each particle gives a teeny tiny push, but they all add up.
The
more crowded
the particles are, the
harder they push
.
The
faster
they are moving, the
harder they push
.Slide13
Pressure in Liquids
Swimming under water you can feel the water pressure.
Pressure in water is due to the
weight
of the water directly above you.
Pressure in liquids depends on depth, NOT on volume of liquid. You feel the same pressure 1m under the surface of a small pool as you would 1m under the surface of a lake. Slide14
Is there
less pressure
or
more pressure
on top of the mountain?
Why?
Because air has weight,
and if there is less air above you,
then there will be less weight.
The weight of the fluid causes the pressure!
More Fluid
Less Fluid
Lower Pressure
Higher PressureSlide15
Plastic bottle sealed at 14,000 feet on Mauna Kea observatory on the island of Hawaii, taken down to 9000 feet and then 1000 where the air pressure is crushing the bottle. Slide16
Force in
Force out
Force out
Force in
Force in
Force in
Force out
Force out
You can’t feel
the atmospheric
pressure because your
body fluids push back!
The forces are balanced.
If air has weight, why don’t we feel the atmospheric pressure?Slide17
Is there more
pressure
on the divers or the shark?
How do you know?
Because water has weight,
and if there is more water above you,
then there will be more weight.
The weight of the fluid causes the pressure!
More Fluid
Less FluidSlide18
What part of an iceberg has the most pressure on it?
Pressure
increases
as you
get
deeper!
Remember
that pressure
pushes in
all directions
so the
iceberg is
being pushed
on all sides,
all the way
around.Slide19
8.3 Buoyancy in Liquids
When an object is in a liquid, the liquid exerts an upward force on it.
This upward force is called the
buoyant forceSlide20
If the weight of the submerged object is greater than the buoyant force, the object will sink.
If the weight of the object is equal to the buoyant force, the object will remain at any level (like a fish).
If the buoyant force is greater than the weight of the object, it will rise to surface and float.Slide21
Weight
of the
boat
Buoyant
Force
Objects float when the forces are balanced!
Objects sink when the forces are unbalanced!
Weight
of the
coin
Buoyant
ForceSlide22
Weight
Buoyant
Force
Buoyant
Force
Weight
When weight is equal to buoyant force, things float.
When weight is more than buoyant force, things sink.Slide23
Objects float when the forces are balanced!
Weight = Buoyant force
Objects sink when the forces are unbalanced!
Weight
>
Buoyant force
weight
buoyant
force
weight
buoyant
force
How do you know if an object will float or sink?Slide24
Archimedes’ Principle
Relationship between buoyancy and displaced liquid.
“An immersed body is buoyed up by a force equal to the weight of the fluid it displaces.
If an immersed body displaces 10 N of fluid, the buoyant force on it will be 10 N.
http://www.youtube.com/watch?v
=yB8c5t8Ct7I&noredirect=1Slide25
Understanding buoyancy
Displacement = pushed aside
Volume of water displaced = the amount of water that is pushed aside when something enters the water.
A completely submerged object always displaces a volume of liquid equal to its own volume.Slide26
Using displacement to determine the volume of an objectSlide27
Sink or Float?
If the weight of the volume of fluid pushed aside is greater than or equal to the weight of an object, the object will float.
Since the object sinks, the weight of the 2 units of liquid displaced must weigh less than the object.Slide28
An immersed body is buoyed up by a force equal to the weight of the fluid it displaces.
The “apparent” weight of an object decreases when immersed in a fluid. Slide29
Floating
A floating object displaces a weight of fluid equal to its own weight. Slide30
Every floating object (ship, submarine, blimp) must be designed to displace a weight of fluid equal to its own weight.
A ship that weighs 10,000 tons must be designed to displace 10,000 tons of water.
A blimp that weighs 100 tons must be designed to displace 100 tons of air. (if it displaces more it rises, less it descends)