1. Chapter 19
Liquids

2. Lucky we have liquids
Earth is just right distance from Sun to allow liquid water on the surface
Most liquids we are familiar with have water as their base
Exceptions: oil-based liquids
Talk about narrow temperature range – talk about us being 70% water – we live in same range as water – some liquid on Titan, but that is only other place in solar system

3. Pressure Review: Pressure = Force/Area P = F/A
Liquids exert force on bottom & walls of container
Reshow Hewitt getting hit on bed of nails

4. Pressure
Pressure depends on density and depth of liquid only, not amount of liquid
3-hole PVC, Hands
P = F/A; P = Density*Depth
Examples – 550 N rock on square base of side 30 cm
A 20 m column of water (density 1000 kg/m3)

5. 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
St. Francis Dam – 1928 – on earthquake fault

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

7. Grooves
Dig to Bedrock & cut channels

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

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

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

11. Ready for Pyramid
Ready for stone!

12. 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

13. Buoyancy Things seem to lose weight in water
Average force Perpendicular
Average forces on bottom at greater depth than at top: net upward force

14. Displacement Principle of Displacement:
Completely submerged object always displaces a volume of liquid equal to its own volume

15. Buoyancy Archimedes Principle:
immersed object is buoyed up by a force equal to the weight of the fluid it displaces

16. 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)

17. Buoy & Archimedes
Buoyancy force does NOT depend on object’s weight, only volume
Buoyancy force same at any depth (unless object is compressed to smaller volume)

18. Should I sink or should I float?
Sinkage* depends on weight of object compared to buoyancy force
W > B – Sink
B > W – Float
B = W – Suspended

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

20. floating, floating, floating along
How do iron/steel boats float?
Principle of flotation – A floating object displaces a weight of fluid equal to its own weight

21. 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

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