Chapter 19 Liquids

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

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

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)

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

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

Grooves Dig to Bedrock & cut channels

Water fill Fill channels with water & mark water level

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

Fill Channels Fill channels with rubble – flat foundation!

Ready for Pyramid Ready for stone!

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

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

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

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

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)

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)

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

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

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

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

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