Ask a question: What is happening? Why?

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Ask a questionWhat is happening? Why?
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Why do these float?
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Density
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What is density?

• Density is a ratio of how much matter there is in
  a certain amount of space.
• A measure of how many particles are packed into a
  certain area.

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More dense more particles in a space Less dense
less particles in a space
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How do I find density?

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

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What instruments do I need?

• To find the volume of the object
• Ruler or graduated cylinder
• Units are cm3 or mL

• To find the mass of an object
• Triple Beam Balance
• Units are grams (g)

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How do I calculate density?

• Density mass OR mass volume.
• volume
• Units for density g/cm3 or g/mL

ALWAYS REMEMBER UNITS!
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Does the sample size affect the density of an
object?

• In other words, if I break off a piece of this
  cube, will it have a different density than the
  whole piece?
• NO!!!

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• 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!!!

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Which one is more dense?

• Which table group is most dense in the classroom?
• How about this Which square is more dense?

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Density of Water

• Water has a density of 1g/mL
• If an object has a density greater than 1g/mL, it
  will sink in water
• If an object has a density of less than 1g/mL, it
  will float in water.

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What do we know about the density of diet coke
vs. coke vs. water?
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Do liquids have different densities?

• Yes! So what happens when you mix them?
• They form layers with the most dense liquid
  falling to the bottom.
• Alcohol .80 g/ml
• Vegetable Oil .90 g/ml
• Water 1.0 g/ml
• Salt Water 1.2 g/ml

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The density of the liquid affects how you float
too!

• Denser liquids help you float more easily.
• That is why it is easier to float in the ocean,
  than in a freshwater lake.

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Illustrating Density
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Metals have different densities

• Lead 11.3 g/cm3
• Aluminum 2.7 g/cm3
• These are all over 1.0 g/ml and most ships are
  made of metal. So how do boats float?

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Explain why one bowling ball floats and one sinks
http//www.youtube.com/watch?vNqNGW0oOXE4
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Density affects many of Earths processes
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Density helps create ocean currents
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Density helps move melted rocks under Earths
crust
crust
mantle
core

• Hot material rises, cooler material sinks,
  creating a current, called a Convection Current

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Solid Land has different densities

• Continental Plates lighter, thicker, (less
  dense) made of granite
• Oceanic Plates heavier, thinner, (more dense)
  made of basalt

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Convergent Boundary

• Plates move toward each other

The more dense oceanic plate subducts under the
less dense continental plate
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Normal and Low bone densities

• Low density bones break more easily.

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Temperature can affect density

• Remember. . . Warm air rises.
• So this means warm air is less dense than cold
  air and it rises

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Density causes your attic to be hot in the summer
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Try it!

• Determine the density of different objects by
  finding their mass and volume, then calculating
  the density.