DENSITY DENSITY

Depends on:Depends on: MassMass VolumeVolume

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

Mass usually expressed in gramsMass usually expressed in grams

Volume usually expressed in cmVolume usually expressed in cm3 3 or or liters, etc.liters, etc.

What would take up more space??? What would take up more space??? A kilogram of feathers….. A kilogram of feathers…..

or a kilogram of steel??or a kilogram of steel??

OR

The proximity of like atoms or The proximity of like atoms or moleculesmolecules

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!!much space an object takes up!!

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

Density is the measure of the Density is the measure of the “compactness” of a material“compactness” of a material

““Compactness”Compactness”

GasesGases How much kinetic energy do the How much kinetic energy do the

molecules have??molecules have?? The greater the kinetic energyThe greater the kinetic energy …… ……the greater the volumethe greater the volume …… …… and the less dense that and the less dense that

gas is!!gas is!!

Therefore, cold air is more dense Therefore, cold air is more dense than warm airthan warm air

GasesGases 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…….

SINK!!!SINK!!!

Balloon and liquid nitrogenBalloon and liquid nitrogen

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/balloon.html#c1

http://paer.rutgers.edu/pt3/movies/http://paer.rutgers.edu/pt3/movies/TVrhoandFb.movTVrhoandFb.mov

www.dkimages.com

LIQUIDSLIQUIDS The more dissolved solids in a The more dissolved solids in a

solution, the more dense (such as solution, the more dense (such as ocean water)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)nutrients, and other substances)

• Kinetic energy again!!Kinetic energy again!!

Denser layers to less dense layers…..

What would happen????What would happen????

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

Lead density = 11340kg/mLead density = 11340kg/m33

Lead floats on liquid mercury!Lead floats on liquid mercury!

SolidsSolids

Ice vs. water…..

SOLIDSSOLIDS

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 layer of ice covering in winter, with water underneath)water underneath)

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

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

Archimedes and the Kings Archimedes and the Kings CrownCrown

Factors affecting DensityFactors affecting Density

TemperatureTemperature

PressurePressure

Factors affecting DensityFactors affecting Density

Dissolved solids – in liquidsDissolved solids – in liquids Concentration and kind of substancesConcentration and kind of substances

FACTORS AFFECTING DENSITYFACTORS AFFECTING DENSITY

ATomS!!!! ATomS!!!!

Relative DensityRelative Density

The density of a material or The density of a material or substance, relative to another substance, relative to another substancesubstance

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 substancesgenerally compare other substances

ALSO known as SPECIFIC GRAVITY ALSO known as SPECIFIC GRAVITY

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….buoyancywater….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 overallwalls, 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 surrounding water at a given depth. surrounding water at a given depth.

Absolute DENSITYAbsolute 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/m1000kg/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 water is at 4water is at 400CC

DETERMINING DENSITYDETERMINING DENSITY Regular Shapes – mass, then Regular Shapes – mass, then

determine the volume by formuladetermine the volume by formulaEX: cubes, cylinders, spheres, EX: cubes, cylinders, spheres,

cones, cones, etc.etc. Irregular shapes – mass, then Irregular shapes – mass, then

measure displacement of a liquid measure displacement of a liquid (usually water) by that irregularly (usually water) by that irregularly shaped objectshaped object