1. Chapter 8
Fluid Mechanics

2. Fluids
Types of matter?
Fluid – any material that flows and changes shape readily

3. Differences between gas & liquids
Gases are easily compressible, liquids are not
Gases fill any 3-D volume, liquid has a more definite volume
Gases are mostly empty space

4. How Dense Can You Be
Density is a physical characteristic of all matter
Amount of Matter in a certain volume
NOT Dependent on total amount of matter you have
Stress ball example – loaf of bread example
Lead bullet vs. cannon ball – same density; swimming pool vs. glass of water

5. Calculating Density (D)ensity = (m)ass / (v)olume
units - kilogram/liter or gram/milliliter
Find the density of 95 kilogram Chris who has a volume of 81 liters.
Gold’s density is 19.3 grams/ml, what is the volume of a 1kg bar?
What is the mass of 2 liters of water
(density 1.0g/ml)?
1.17 kg/L;
51.8ml or 51.8 cm3 – square side 7.2 cm;
2000 grams or 2 kg (4.4 lbs)

6. Density Solids & liquids tend to be incompressible
Gases very compressible
loaf of bread
trash compactor

7. Pressure Review: Pressure = Force/Area P = F/A
Unit is Pascal (Newton/m2)
Find your own pressure – 1 foot, tip of shoe, 2-hand stand

8. Pressure
Pressure depends on density and depth of fluid only, not amount of fluid
P = density*depth
Demo hands, holey cup, finger in the levee

9. Dams How do you build a good dam? Dam disasters in US Johnstown Flood
Thick bottom …
toward lake
arched (top of arch toward lake)
Dam disasters in US
Johnstown Flood
St. Francis Dam
Show the picture of Hoover dam
Johnstown flood – 2000 killed 1889 – best of Modern Marvels 2, Episode 8 – 20 minutes?
St. Francis Dam – 1928 – on earthquake fault

10. Can You Feel the Pressure II
Difference – gases are compressible – air is surface thin at great height
Pressure difference is greater than liquids because density is different
Pike’s Peak bottle 10N/cm2 or 14 lb/inch2 – get steel pressure bar

11. Difference in Pressure
NATURE DOESN’T SUCK!!!!
Examples
Scuba Diving
Drinking from a straw
Vacuum cleaner
‘Suction’ Cups
Scuba bubbles – the bends -
Extra credit project – tallest straw – how you made it – bring it in
NEITHER DOES PHYSICS!!!!!!!!!!!

12. Measuring Pressure
Barometers used to measure
Pressure
Elevation

13. Barometer
Two Types
Simple Barometer – Glass tube fills as air pressure increases

14. Other Barometer Two Types
Aneroid Barometer – Uses Pressure difference between inside and outside

15. Don’t Break the Law Boyle’s Law Uses of pressure
Pressure x Volume is constant at constant temperature
Pressure is proportional to density
- tires
Uses of pressure
Building bridges/subways

16. Usefulness of Water ‘Water seeks its own level’ Egyptians VS
Why did Pyramid not lean? VS

17. Grooves
Dig to Bedrock & cut channels

18. Water fill
Fill channels with water & mark water level

19. Cut to Mark
Drain water & cut bedrock down to the mark

20. Fill Channels
Fill channels with rubble – flat foundation!

21. Ready for Pyramid
Ready for stone!

22. Usefulness of Water ‘Water seeks its own level’ Egyptians Construction
Drop ceilings
Talk about using a level, use Pascal’s vase, talk about leveling pyramids
Use level and plastic tubing

23. Buoyancy Things seem to lose weight in water Water is stupid
Average forces on bottom at greater depth than at top: net upward force (independent of depth)

24. Principle of Displacement
Completely submerged object always displaces a volume of liquid equal to its own volume
Archimedes – immersed object is buoyed up by a force equal to the weight of the fluid it displaces
Archimedes’ Principle

25. Example
Archimedes – immersed object (chunk of iron) pushed up by a force equal to the weight of the fluid it displaces (water in other container)

26. Should I sink or should I float?
Sinkage* depends on weight of object compared to buoyancy force
Submerged:
W > B – Sink
B > W – Rises (to surface, see below)
B = W – Suspended
On the surface (floating)
W=B always!!!!!!!!!!!

27. How to make a boat out of materials more dense than water
Steel boats?
Shape the steel so that air is added and the density falls below that of water

28. Should I sink or should I float?
Submarines
Life jackets
Fish
Crocodiles
Divers
Oil

29. Pascal, Pascal ya Rascal
Pascal’s principle – changes in pressure at any point in an enclosed fluid at rest are transmitted to all points in the fluid and act in all directions

30. Pascal Examples
Hydraulics – brakes, lifts, it is a machine!

31. It’s the Principle Bernoulli’s Principle
when fluid is confined – speed increases
when speed of fluid increases - pressure drops
Water hose
Water out of a hose – put finger over it to increase the pressure

32. Exotic uses of Bernoulli
Lift of an object occurs when PressureAbove < PressureBelow
Airplanes – Use bernoulli …
But also use Newton’s 3rd law
2 ways plane flies

33. FAST CARS Formula 1 cars need wings!! …to keep them on the ground
Upside down wings
Upside down to keep on road 100mph can drive upside down, pass in tunnel?

34. Every Day examples of Bernoulli
Birds
Tornados/Hurricanes & houses
Baseball pitches
Umbrellas
Shower curtain
2 ways plane flies