Transcript Properties of Liquids

Properties of Liquids:
Density and Buoyancy
Definitions
Density:
The mass per unit
volume of a material.
Buoyancy:
The ability of a fluid to
exert an upward force
on a floating object.
Density
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The symbol for density
is usually D and has
units of g/cm3.
Density is a physical
property of a material.
Often, a material’s
density is used to
identify it.
Densities of Common
Materials
Water
1.00 g/cm3
Aluminum
2.7 g/cm3
Steel
7.9 g/cm3
Gasoline
.70 g/cm3
Mercury
13.6 g/cm3
Air
.0013 g/cm3
Density
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Solids, liquids, gases, and
other phases of matter all
have densities.
Solids are most dense,
liquids next dense, and
gases least dense
MOST of the time, density is
inversely related to
temperature.
D=
=
m
V
Which weighs more,
A pound of feathers or a pound of lead?
Which is more dense?
Calculating Densities
Mass of the Sun:
2 x 1030 kg
Volume of the Sun:
1.4 x 1027 m3
Average Density of the Sun:
1.4 g/cm3
Calculating Densities
Mass of the Earth:
6 x 1024 kg
Volume of the Earth:
1.1 x 1021 m3
Average Density of Earth:
5.5 g/cm3
Does it make sense that
the Earth is more dense
than the Sun?
A Density Problem:
Does this help?
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You found this ring on the track at
your school. You wondered what it
was made of.
You calculated it’s density to be
approximately 7.9 g/cm3.
What is it made of?
Metal
Density g/cm3
Aluminum
2.70
Gold
19.30
Copper
8.63
Steel
7.87
Silver
10.40
Chromium
7.10
Lead
11.30
Forces
Newton’s Laws:
1.) The law of inertia: An object in
motion stay in motion until it is
acted upon. Or, an object at rest
stays at rest until acted upon.
2.) F = m*a
3.) When two bodies interact by a
force, the force on the first body
is equal in magnitude and
opposite in direction to the force
on the second body.
Archimedes’ Principle
The buoyant force
exerted on an object
submersed in a fluid is
equal to the weight of
the fluid displaced.
But what does that mean?!?
Fb = D*V*g
Fb : Buoyant force
V : Volume of fluid displaced
D : Density of fluid
g : Acceleration due to
gravity
Fbuoyant
Wobject
Why does it float?
For an object to
float:
Fbuoyant
Wobject = Fbuoyant
Wobject
Buoyancy
Calculations
The polar bear on ice:
A 500 kg polar bear sees
a slab of ice floating by
and tries to hop on. The
ice has a volume of 4
m3 and a density of .92
g/cm3. Seawater has a
density of 1.035 g/cm3.
Does the polar bear
float away happily?
Not this time!
Fb = 4140 N < Wbear = 4900N
Activity
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You will determine the density of a liquid and
use that density to identify the liquid.
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Good luck!
Questions?