Chapter 4: Density and Buoyancy
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Density: Investigation 4A
What is density and how is it measured?
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1. Density.
a. describes how much mass is in a given volume of a material
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b. Solids, liquids and gases are matter, so they all have density.
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c. The units used for density depends on whether the substance is solid
or liquid.
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______________________
______________________
- For liquids use units of grams per milliliter (g/mL)
- For solids use density in units of g/cm3
Practice: Plastic’s density is greater that water’s density, but the bath toy
floats. Why is this?
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d. Density is a property of material that is independent of quantity or
shape.
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e. density changes for different substances because:
i. Atoms have different masses.
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ii. Atoms may be “packed” tightly or loosely.
f. Liquids tend to be less dense than solids of the same material.
i. Water is an exception to this rule. The density of solid water,
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or ice, is less than the density of liquid water.
Think: Why might this be important for sea life where lakes
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______________________
freeze in the winter?
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2. Volume
a. the amount of space an object takes up.
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b. The volume of a rectangular solid is found by multiplying length
times width times height.
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width
height
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length
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c. Use a graduated cylinder to measure the volume of a liquid.
d. To measure the volume of an irregular shape, use a technique called
______________________
displacement.
______________________
i. put the object in water and measure the amount of water
displaced (how much did the volume change?)
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3. Finding Volumes of Common Shapes
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.
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Buoyancy: Investigation 4B sink or float
Steel is more dense than water so why do steel boats float?
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1. Weight
a. Weight is a force, like any other pushing or pulling force,
and is caused by Earth’s gravity.
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______________________
b. it is easy to confuse mass and weight, but they are not the
same.
c. Weight is the downward force of gravity acting on mass.
______________________
______________________
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2. Buoyancy
a. Buoyancy is a measure of the upward force a fluid exerts on
______________________
______________________
an object that is submerged.
b. The strength of the buoyant force on an object in water
depends on the volume of the object that is underwater.
______________________
______________________
More volume
underwater
Less volume
underwater
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______________________
c. In the third century BC, a Greek mathematician named
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______________________
______________________
Archimedes realized that buoyant force is equal to the weight
of fluid displaced by an object.
d. A simple experiment can be done to measure the buoyant
force on a rock with a spring scale.
______________________
______________________
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e. Buoyancy explains why some objects sink and others float.
Buoyant force is
stronger than weight 
Object floats
Weight is stronger
than buoyant force 
Object sinks
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3. Practice Problem – Buoyancy
a. What is the buoyant force on a rock with a volume of 1,000 cm3?
1. In air, the scale shows the rock’s weight as 29.4 newtons.
2. When the rock is completely submerged, the scale reads 19.6
newtons.
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______________________
3. The difference is a force of 9.8 newtons. This is the buoyant
force!
4. Density and buoyancy
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______________________
a. If you know an object’s density you can quickly predict whether it
will sink or float.
b. Average density determines whether objects sink or float.
- An object with an average density GREATER than the density
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of the liquid will sink.
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______________________
- An object with an average density LESS than the density of the
liquid will float.
c. steel boats can be made to float because their density is less than water
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______________________
d. a loaded cargo ship will sit lower in the water than an unloaded ship
nearby.
- A full ship has more mass than an empty ship.
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- A full ship must displace more water (sink deeper) to make the
buoyant force large enough to balance the ship’s weight.
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Summary – fill up
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this section!
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Density
Essential Question  What is density and how is it measured?
1. Density.
a. describes how much ____________ is in a given volume of a material
b. Solids, liquids and ____________ are matter, so they all have density.
c. The ____________ used for density depends on whether the substance is
solid or liquid.
- For _______________ use units of grams per milliliter (g/mL)
- For _______________ use density in units of g/cm3
Practice: Plastic’s density is greater that water’s density, but the bath toy
floats. Why is this?
_____________________________________________________________
_____________________________________________________________
d. Density is a property of material that is independent of quantity or
_________________.
e. density changes for different substances because:
i. Atoms have different ___________________.
ii. Atoms may be “packed” __________________ or loosely.
f. Liquids tend to be ______________ dense than solids of the same
material.
i. _________________ is an exception to this rule. The density
of solid water, or ice, is less than the density of liquid water.
Think: Why might this be important for sea life where lakes
freeze in the winter?
_____________________________________________________________
_____________________________________________________________
2. Volume
a. the amount of ___________________ an object takes up.
b. The volume of a rectangular solid is found by multiplying length times
width times ___________________.
width
height
length
c. Use a graduated cylinder to measure the volume of a ________________.
d. To measure the volume of an ___________________ shape, use a
technique called displacement.
i. put the object in water and measure the amount of water
___________________________ (how much did the volume change?)
3. Finding Volumes of Common Shapes
.
Summary – no I, you, me us, etc. Tell a factual story of your notes.
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Buoyancy:
Essential Questions 
Will it sink or float? If steel is more dense than water,
why do steel boats float?
1. Weight
a. Weight is a ______________, like any other pushing or
pulling force, and is caused by Earth’s _______________.
b. it is easy to confuse mass and weight, but they are _______
the same.
c. Weight is the downward force of gravity acting on mass.
2. Buoyancy
a. Buoyancy is a measure of the _________________ force a
fluid exerts on an object that is submerged.
b. The ____________________ of the buoyant force on an
object in water depends on the ________________ of the
object that is underwater.
Less volume
underwater
More volume
underwater
c. In the third century BC, a Greek mathematician named
Archimedes realized that buoyant force is ________________
to the weight of fluid _____________________ by an object.
d. A simple experiment can be done to measure the buoyant
force on a rock with a spring scale.
e. Buoyancy explains why some objects _______ and others
_____________.
Buoyant force is
stronger than weight 
Object floats
Weight is stronger
than buoyant force 
Object sinks
3. Practice Problem – Buoyancy
a. What is the buoyant force on a rock with a volume of 1,000 cm3?
1. In air, the scale shows the rock’s weight as _______________.
2. When the rock is completely ________________, the scale
reads 19.6 newtons.
3. The difference is a force of 9.8 newtons. This is the
___________ force!
4. Density and buoyancy
a. If you know an object’s __________________ you can quickly
predict whether it will sink or float.
b. Average density determines whether objects sink or ______________.
- An object with an average density ___________________ than
the density of the liquid will sink.
- An object with an average density ______________ than the
density of the liquid will float.
c. steel boats can be made to float because their density is ___________
than water
d. a ____________________ cargo ship will sit lower in the water than
an unloaded ship nearby.
- A full ship has more _________________ than an empty ship.
- A full ship must _____________ more water (sink deeper) to
make the buoyant force large enough to balance the ship’s weight.
Summary – no I, you, me us, etc. Tell a factual story of your notes.
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