Density

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Density

• Mrs. Reese

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What is density?

• 1. Density is the measurement of the compactness
  of an object.
• 2. Density is a physical property that is
  determined by the ratio of a substances mass to
  its volume.
• 3. Mass is how much matter is inside of an
  object.
• 4. Volume is how much space something takes up.

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Density

• All substances (solids, liquids, or gases) have
  unique densities.
• Density is a GREAT way to indentify unknown
  substances!

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Which one is more dense?

• Demonstration People in a square
• How about this Which square is more dense?

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Which one is more dense?

• Now which one is more dense?

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What is density?

• Density mass OR mass volume.
• volume
• Units for density g OR g .
• cm3 ml

ALWAYS REMEMBER UNITS!
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How can density be affected?

• There are some factors such as change in
  temperature or state of matter that can affect
  the density of matter.
• As a GENERAL RULE, solids tend to be more dense
  than liquids or gases because their atoms are
  more compacted within equal volume.
• EX Liquid gold has a density of 17.3 g/ml while
  solid gold has a density of 19.3 g/cm3.

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There is ALWAYS an exception!
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There is ALWAYS an exception

• When you freeze water, the density of the ice is
  LESS than the density of water (even though they
  are both the same substance). When you freeze
  ice, it crystallizes and leaves more gaps which
  increases the volume (by about 9) and therefore
  the density goes down.
• THUS, ICE CAN FLOAT IN WATER!

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Water vs. Ice
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How can density be affected?

• Example Hot air balloon
• When you heat a gas, it expands (increasing
  its volume) and therefore decreasing its density.
  Warmer air rises because its density is less
  than the surrounding air.

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CAREFUL!

• Cutting an object into pieces WILL NOT change its
  density. You have not changed the particle
  compaction in any way!
• Example If the density of a piece of American
  red oak wood is .74 g/cm3. If you cut the piece
  of would in half, the density would NOT decrease
  by two, IT WOULD STAY THE SAME!

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What can float on water?

• Density of water is 1.0 g/ml
• If the density is greater than 1.0 g/ml, then the
  object will sink in water.
• If the density is less than 1.0 g/ml, then the
  object will float in water.

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Explain this.

• Why does the ice cube float in beaker 1 and not
  in beaker 2?

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Liquid Layers

• If you pour together liquids that dont mix and
  have different densities, they will form liquid
  layers.
• The liquid with the highest density will be on
  the bottom.
• The liquid with the lowest density will be on the
  top.

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Liquid Layers

• Which layer has the highest density?
• Which layer has the lowest density?
• Imagine that the liquids have the following
  densities
• 10g/cm3 3g/cm3
• 6g/cm3 5g/cm3
• Which number would go with which layer?

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Liquid Layers Try with your neighbor

• Which liquid has the highest density?
• Which liquid has the lowest density?

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On your own

• Your friends at your lunch table all have
  different stuff in their lunch. Liquid A has a
  density of 1.07 g/ml, Liquid B has a density of
  0.98 g/ml, Solid C has a density of 1.12 g/cm3,
  and Mush D has a density of 1 g/cm3. You decide
  to make a gross combination of the four in your
  water bottle. Which order will they appear in,
  from bottom to top?
• a) Solid C, Mush D, Liquid A, and Liquid B on
  top?
• b) Solid C, Mush D, Liquid B, and Liquid A on
  top?
• c) Solid C, Liquid A, Mush D, and Liquid B on
  top?
• c) Liquid A, Liquid B, Solid C, and Mush D on top?

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5 special steps-thats all you need!
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Lets try a density problem together

• Frank has a paper clip. It has a mass of 9g and a
  volume of 3cm3. What is its density?
• Frank also has an eraser in the shape of a
  cube. It has a mass of 3g, and each side of the
  eraser is 1.0 cm long. What is its density?

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Work on these problems with your neighbor.

• Jack has a rock. The rock has a mass of 6g and
  the volume of the water level went up from 50 ml
  to 53 ml when placed inside. What is the density
  of the rock?
• Jill has a gel pen. The gel pen has a mass of 8g
  and a volume of 2cm3. What is the density of the
  gel pen?

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Now, try these on your own.

• AlLicia has a watch. It has a mass of 4g and a
  volume of 2cm3. What is the density of the watch?
• A cube made of very old hard wood, has a mass of
  45g and measures 6cm a side, will it sink or
  float?
• Mia has a wallet. It has a mass of 15g and a
  volume of 5cm3. What is the density of the
  wallet?
• A block has a mass of 20g and measures
  2cmX4cmX2cm, will it sink or float?

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Try these on your own

• From their density values, decide whether each of
  the following substances will sink or float when
  placed in sea water, which has a density of 1.025
  g/mL.
• Gasoline 0.66 g/mL Asphalt l.2 g/mL
• Mercury 13.6 g/mL Cork 0.26 g/mL