Transcript Density Notes - Jamestown School District

DENSITY
Goal: To measure density using
the proper units and equipment
What is density?
• Density is:
The number of particles
packed into a space
• Formula:
Density = Mass/Volume
How do you calculate density?
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Mass of object (grams)
Volume of object (ml or cm3)
Mass divided by volume
Round to nearest tenth
Label answer (g/ml or g/cm3)
Density Example
• Density = Mass/Volume
• Example 1:
–The mass of a block is 100 g.
The volume of the block is 5
cm3. What is the block’s
density?
ANSWER:
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M= 100g
V= 5 cm3
D = m/v
D= 100g / 5 cm3
D= 20.0 g/cm3
Example 2
• The mass of a rock is 20.5 g. The volume
of the rock is 41.0 ml. What is the rock’s
density?
• M= 20.5 g
• V= 41.0 ml
• D= m/v = 20.5 g / 41.0 ml
• D= 0.5 g/ml
DENSITY
• When you find the density of an object, the
number you calculate tells you whether the
object will sink or float when placed in
water.
• Density of water= 1 g/ml
• Less dense items float in water
• More dense items sink in water
So……………
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Density > 1 g/ml, the object will sink
Density < 1 g/ml, the object will float
Here’s an example
A toy car with a mass of 20 g and a volume of 10
ml would have a density of what?
Density = 20/10 = 2 g/ml
Would this sink or float in water?????????
SINK- Why?
It’s density is greater than 1 g/ml.
Example
• A bar of soap has a mass of 15 g and a
volume of 45 cm^3. Will it sink or float
when placed in water?
• FLOAT- Why?
• It has a density of .3 g/cm^3, which is less
than 1, the density of water
Which objects will sink or float?
HOLD UP SINK IF THE
OBJECT WILL SINK,
HOLD UP FLOAT IF THE
OBJECT WILL FLOAT
What will sink or float in water?
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Penny
Egg
Pencil
Iron
Pumice
Silver
Rock
1.3 g/ml
0.9 g/ml
1.6 g/ml
4.8 g/ml
0.7 g/ml
3.2 gml
1.1 g/ml
Density of liquids
• What will liquids with different densities do
when poured into the same jar?
• They will layer according to density
• Liquids with higher densities will go to the
bottom, liquids with lower densities will
float to the top
• Look at the example on the front counter
Example on counter
• The jar contains the following:
• Which layer is which then?
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Water = 1 g/ml
Oil = 0.7 g/ml
Syrup = 3.2 g/ml
Liq. Soap = 2.5 g/ ml
• Draw a picture in your notes and label it
with the correct name of each liquid
Which is which?
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Top = Oil
2nd = Water
3rd = Soap
Bottom = Syrup
Example
• Please draw a picture of how the following
liquids would layer out in a jar:
• Mercury = 5.6 g/ml
• Italian dressing = 0.7 g/ml
• Water = 1 g/ml
• Antifreeze = 1.4 g/ml
• Paint thinner = 0.3 g/ml
Answer:
Top= PAINT THINNER
• ITALIAN DRESSING
• WATER
• ANTIFREEZE
Bottom =MERCURY
Is there a way to estimate
density?
• You can estimate density by putting the
object in water
• If it sinks d > 1 g/ml
• If it floats d < 1 g/ml- see how much of the
object is below the water
• Remember: Density corresponds to the
amount of the object below the water’s
surface !
• Look at the block on the front counter.
What is it’s approximate density???
• What would happen to the density of this
block if I were to cut in in half?
• How about if I cut it into six pieces?
• NOTHING WOULD HAPPEN TO ITS
DENSITY!!
• Density of an object remains the same even
when the object is cut into smaller pieces
• An object’s density always remains the
same !!!!
• The density of copper is always 8.9 g/mlno matter how big or small!
• The density of Nylon is always 1.13 g/mlno matter how big or small !
• Density can help identify what a material is
made of !!!
Last Example
• A cube has a mass of 14.3 g and a volume
of 5.3 ml. What is the cube made of?
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Copper 8.9 g/ml
Acrylic 1.17 g/ml
Oak 0.7 g/ml
Aluminum 2.7 g/ml