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..ArchimedesArchimedes picpic

lorlor!!

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ArchimedesArchimedes Archimedes was an ancient GreekArchimedes was an ancient Greek

scientist who discovered thatscientist who discovered thatfloating objects are supported by anfloating objects are supported by anupward force calledupward force called buoyancybuoyancy. ( P.S.. ( P.S.--

he discovered this while taking ahe discovered this while taking abath, and decided to run through thebath, and decided to run through thestreets shouting out Eureka,streets shouting out Eureka,Eureka!)Eureka!)

Buoyant force is equal to the weightBuoyant force is equal to the weightof the liquid that the force displaces.of the liquid that the force displaces.

The theory concerning buoyancy isThe theory concerning buoyancy is

called Archimedes Principle.called Archimedes Principle.

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BuoyancyBuoyancyWhy do some objects float, while otherWhy do some objects float, while other

objects sink?objects sink?

A coin sinks because it weights moreA coin sinks because it weights morethan the water it displaces.than the water it displaces.

The aluminum ball floats because itThe aluminum ball floats because itcontains air within its folds.contains air within its folds.

Air weighs less than water, so the ballAir weighs less than water, so the ballweighs less than the water itweighs less than the water it

displaces.displaces.

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TitanicTitanic

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Why did theWhy did the

Titanic Sink?Titanic Sink? After it hit the iceberg, water beganAfter it hit the iceberg, water began

to fill the air filled compartments onto fill the air filled compartments onthe ship.the ship.

The added weight of the water,The added weight of the water,combined with the weight of the shipcombined with the weight of the ship

became greater than the buoyantbecame greater than the buoyantforce supporting the ship.force supporting the ship.

We all know what happened afterWe all know what happened afterthat!that!

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Archimedes Principle

!! bbuoyant FF gm fluiddisplaced

gVF submergedb V

The magnitude of the buoyant force is given byArchimedes Principle. It states that when An

object fully or partially immersed in a fluid is

buoyed up by a force that is equal to the

_______ of the ___________________.weight displaced fluid

submergedfluiddisplaced VmVmSince VV !! , subm rg dfluiddis pla d mmSin VV ,

V= density ofthe displacedfluid

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Objects that Float:

!___F

Objects that Sink:

bobj t FW __

fluobj t VV __So

0

Weightobject = Fb=Weightdisplaced fluid

>

>

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Imagine a very light,

thin-walled sack filled

with water that is inequilibrium in a pool.

Clearly, there must be an _______ force

exerted on the sack to balance its weight (thepull of gravity down)

This upward force is

actually the vector sum of allthe forces acting on the

object due to the

surrounding water, and is

called the _________ force.Pressure is greater

on bottom of sack!

upward

buoyant

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How do boats/ships float?O

bviously the density of a metal rowboat or aconcrete canoe is greaterthan the density

of water, but they float because they contain

a large amount of empty space. Because of

their _______, they displace enough water tobalance their own weight.

shape

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How do Submarines Dive & Surface?Does the buoyant force change? ____!

A sub has ballast tanks that can

be filled with _______ or _____.

To dive, a sub must become heavier, so the tanks

allow _______ in while venting ____ out.

To surface, a sub must become lighter. A supply of

compressed air on the sub is used to force ______

back out of the ballast tanks.

NO

water air

water air

water

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Hot Air Balloons

Ifballoon is floating (notaccelerating up or down):

________!bF

(includes the weight of

the balloon, the basket,the riders, and the __________ balloon!)

Wtotal

airinside the

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Water Bridge in Germany

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The endThe end