Ask a question:Ask a question:What is happening? Why?What is happening? Why?

Why do these float?Why do these float?

DensityDensity

What is density?What is density? Density is a ratio of Density is a ratio of how muchhow much

mattermatter there is in a certain there is in a certain amount amount of spaceof space..

A measure of how many particles A measure of how many particles are packed into a certain area.are packed into a certain area.

More dense = more particles in a spaceLess dense = less particles in a space

How do I find density?How do I find density?

I need to find out how much stuff (mass) is in I need to find out how much stuff (mass) is in a certain amount of space (volume)a certain amount of space (volume)

What instruments do I need?What instruments do I need?

To find the mass of To find the mass of an objectan object Triple Beam Triple Beam

BalanceBalance Units are gUnits are g

To find the volume To find the volume of the objectof the object Ruler or graduated Ruler or graduated

cylindercylinder Units are cmUnits are cm33 or mL or mL

How do I calculate density?How do I calculate density?

Density = Density = mass mass OR mass ÷ volume. OR mass ÷ volume.

volumevolume

Units for density: Units for density: g g or or g g

cmcm3 3 m lm l

ALWAYS REMEMBER

UNITS!

Does the sample size affect the Does the sample size affect the density of an object?density of an object?

In other words, if I In other words, if I break off a piece of break off a piece of this cube, will it have this cube, will it have a different density a different density than the whole than the whole piece?piece?

NO!!!NO!!!

Density is based on total mass divided by total volume.

When one changes, the other also changes, so the density (which is a ratio) stays the same!!!

Which one is more dense?Which one is more dense?

Which table group is most dense in the Which table group is most dense in the classroom?classroom?

How about this: Which square is more dense?How about this: Which square is more dense?

Density of WaterDensity of Water Water has a density of 1g/mLWater has a density of 1g/mL If an object has a density greater than 1g/mL, If an object has a density greater than 1g/mL,

it will sink in waterit will sink in water If an object has a density of less than 1g/mL, it If an object has a density of less than 1g/mL, it

will float in water.will float in water.

What do we know about the What do we know about the density of diet coke vs. coke vs. density of diet coke vs. coke vs.

water?water?

Do liquids have different Do liquids have different densities?densities?

Yes! So what happens when you mix Yes! So what happens when you mix them?them?

They form layers with the highest density They form layers with the highest density falling to the bottom.falling to the bottom.

Alcohol = .80 g/mlAlcohol = .80 g/ml Vegetable Oil = .90 g/mlVegetable Oil = .90 g/ml Water = 1.0 g/mlWater = 1.0 g/ml Salt Water = 1.2 g/mlSalt Water = 1.2 g/ml

The density of the liquid The density of the liquid affects how you float too!affects how you float too!

Denser liquids help you float more easily. Denser liquids help you float more easily. That is why it is easier to float in the That is why it is easier to float in the

ocean, than in a freshwater lake.ocean, than in a freshwater lake.

Illustrating DensityIllustrating Density

Metals have different densitiesMetals have different densities Lead 11.3 g/cmLead 11.3 g/cm33

Aluminum 2.7 g/cmAluminum 2.7 g/cm33

These are all over 1.0 g/ml and most ships These are all over 1.0 g/ml and most ships are made of metal. So how do boats float?are made of metal. So how do boats float?

http://www.youtube.com/watch?v=NqNGW0oOXE4

Explain why one bowling ball Explain why one bowling ball floats and one sinksfloats and one sinks

Density affects many of Earth’s Density affects many of Earth’s processesprocesses

Density helps create ocean currentsDensity helps create ocean currents

Density helps move melted rocks Density helps move melted rocks under Earth’s crustunder Earth’s crust

Hot material rises, cooler material sinks, Hot material rises, cooler material sinks, creating a current, called a creating a current, called a Convection Convection CurrentCurrent

core

mantle

crust

Solid Land has different densitiesSolid Land has different densities Continental Plates – lighter, thicker, made of Continental Plates – lighter, thicker, made of

granitegranite Oceanic Plates – heavier, thinner, made of Oceanic Plates – heavier, thinner, made of

basaltbasalt

Convergent BoundaryConvergent Boundary

Plates move toward each otherPlates move toward each other

The more dense oceanic plate subducts under the less dense continental plate

Normal and Low bone densitiesNormal and Low bone densities Low density bones break more easily.Low density bones break more easily.

Temperature can affect Temperature can affect densitydensity

Remember. . . Warm air rises. Remember. . . Warm air rises. So this means warm air is less dense than So this means warm air is less dense than

cold air and it risescold air and it rises

Density causes your attic to be hot in Density causes your attic to be hot in the summerthe summer