density.ppt 2225KB Jun 23 2011 10:31:36 AM

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DENSITY

 Depends on:Depends on:

 MassMass  VolumeVolume

D = m/v (g/cmD = m/v (g/cm33))

Mass usually expressed in grams Mass usually expressed in grams

Volume usually expressed in cm

Volume usually expressed in cm3 3 or or

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What would take up more space???

A kilogram of feathers…..

or a kilogram of steel??

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 The proximity of like atoms or The proximity of like atoms or molecules

molecules

 More than just the “heaviness” of a More than just the “heaviness” of a substance, density includes how

substance, density includes how

much space an object takes up!!

 All substances have density including All substances have density including liquids, solids, and gases

liquids, solids, and gases

Density is the measure of the

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“

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Gases



How much kinetic energy do the

molecules have??



The greater the kinetic energy



……

the greater the volume



……

and the less dense that

gas is!!



Therefore, cold air is more dense

than warm air

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Gases

 Real life application…..Real life application…..

 Low pressure weather system means Low pressure weather system means

warmer air tends to rise, warmer air tends to rise,

 High pressure systems indicate a colder High pressure systems indicate a colder

more dense air mass that will……. more dense air mass that will…….

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Balloon and liquid nitrogen

 http:http://hyperphysics//hyperphysics..phy-astrphy-astr..gsugsu..

edu/hbase/thermo/balloon

edu/hbase/thermo/balloon.html#c1.html#c1  http://paer.rutgers.edu/pt3/movies/Thttp://paer.rutgers.edu/pt3/movies/T

VrhoandFb.mov

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LIQUIDS

 The more dissolved solids in a The more dissolved solids in a

solution, the more dense (such as

ocean water)

 Cold water in lakes tend to sink (this Cold water in lakes tend to sink (this creates a constant mixing of water,

creates a constant mixing of water,

nutrients, and other substances)

• Kinetic energy again!!_{Kinetic energy again!!}

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What would happen????

 Mercury density = 13600kg/mMercury density = 13600kg/m3 ₃

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Solids

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SOLIDS

 Ice is less dense than water (which is Ice is less dense than water (which is why lakes and ponds have a thin

why lakes and ponds have a thin

layer of ice covering in winter, with

water underneath)

 Various rocks, woods, metals have a Various rocks, woods, metals have a characteristic density specific to that

characteristic density specific to that

substance

Wouldn’t you like to have a bunch of THIS dense

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Archimedes and the Kings

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Factors affecting Density

 TemperatureTemperature

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Factors affecting Density

 Dissolved solids – in liquidsDissolved solids – in liquids

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FACTORS AFFECTING DENSITY

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Relative Density

 The density of a material or The density of a material or

substance, relative to another

substance

 Expressed in a ratio: water = 1g/ccExpressed in a ratio: water = 1g/cc

 Water is the substance to which we Water is the substance to which we generally compare other substances

generally compare other substances

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 How are Submarines like fish…. How are Submarines like fish….

 The swim bladder in bony fish control their The swim bladder in bony fish control their

relative density in order to rise or dive in the relative density in order to rise or dive in the

water….buoyancy water….buoyancy

 When air is added to the swim bladder, by When air is added to the swim bladder, by

diffusion through the blood vessels in the bladder diffusion through the blood vessels in the bladder

walls, the fish becomes less dense overall walls, the fish becomes less dense overall

 when air is removed fish become more densewhen air is removed fish become more dense

 By changing the volume of air in the bladder, the By changing the volume of air in the bladder, the

fish’s density can be made equal to that of the fish’s density can be made equal to that of the

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Absolute DENSITY

 The density of a material in its The density of a material in its closest “packed form”

closest “packed form”

 For water: Absolute Density = For water: Absolute Density = 1000kg/m

1000kg/m33

at 4at 400C and 1 atm(pressure)C and 1 atm(pressure)

in other words, the greatest density of in other words, the greatest density of

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DETERMINING DENSITY

 Regular Shapes – mass, then Regular Shapes – mass, then

determine the volume by formula

EX: cubes, cylinders, spheres,

cones,

cones, etc._etc.

 Irregular shapes – mass, then Irregular shapes – mass, then

measure displacement of a liquid

(usually water) by that irregularly

shaped object