Transcript Properties of Solids and Fluids final post version

Properties of Solids and Fluids
Density
• Density is a property that describes the
relationship between mass and volume.
Density (g/cm3)
m
D
V
Mass (g)
Volume (cm3)
•
•
Density describes how tightly packed the
atoms or molecules in a substance.
The density of a pure substance is the
same regardless of the form.
Note: Both the paper clip and bike cable
are made of steel
Calculate the density
• What is the density of a piece of wood that
has a mass of 25 grams and a volume of 29.4
cm3?
• D (density) = mass (mass in grams) / V
(volume in cm3
• D = 25 grams/ 29.4 cm3 = .850 g/cm3
Properties of Solids
• Hardness: measure of solid’s resistance to
scratching.
• Elasticity: measure of a solid’s ability to be
stretched and return to its original size.
• Brittleness: measure of solid’s ability to
shatter upon impact
• Malleability: measure of solid’s ability to be
pounded into thin sheets
• Tensile strength: measure of how much pulling
a solid can withstand without breaking.
Fluids: Liquids and Gases
Viscosity
Buoyancy
Archimede’s Principle
Density of Fluids
• Since the atoms in a liquid are
not as neatly stacked as the
atoms in a solid are, the liquid
tends to take up more space.
• As a result, liquids are typically
less dense than solids.
That Crazy Water!
• Water is unusual and an
exception. Ice (solid form)
is less dense than the
liquid form. Therefore, ICE
FLOATS.
• Frozen water molecules
freeze into ice crystals that
are mostly empty space.
The molecules are more
tightly packed in water’s
liquid form.
Buoyancy and Archimedes Principle
• A buoyant force is an upward force exerted on an
object by a fluid in which the object is immersed.
When an object is placed in a fluid, the object
displaces some of the fluid. The volume of the fluid
displaced is equal to the volume of the object.
• Archimede’s principle - an object in a fluid is acted on
by a buoyant force equal to the weight of the fluid
displaced by the object
• Demonstration
Viscosity
• Viscosity is a property of gases and liquids.
• Viscosity is a measure of the material’s
resistance to flow.
• High viscosity fluids take longer to pour from
their containers than low viscosity fluids.
• Demonstration
Why are some liquids more
viscous than others?
• Viscosity is determined by the
shape and the size of the
molecules in the liquid.
• Larger molecules create more
friction than small, smooth
molecules.
• Liquids with large molecules will
flow at a slower rate than liquids
made up of small molecules.
Gases
Charles’ Law
Boyle’s Law
Pascal’s Principle
Bernoulli’s Principle
Density of gases
• Gases are always less dense than solids or
liquids
• Density of gases depends upon the molecular
weight of the gas particles
• If a gas is lighter than air, it rises above the air
and if it is heavier it sinks through the air to
the ground
Behavior of Gases
• Charles’ Law says that a volume of a gas will
increase with increasing temperature.
• As the air in a hot air balloon is heated, volume of
the balloon increases. As a result, the density of the
air inside the balloon decreases.
• A hot air balloon will rise because the density of the
air inside the balloon is less dense than the air
surrounding the balloon.
Boyle’s Law
• If you squeeze the same amount of gas in a
smaller container, the gas particles collide
with the walls of the container more often,
increasing the pressure.
• Boyles law says as the
pressure of a gas increases
its volume decreases
proportionally.
Pressure
• Pressure is the force of the fluid acting on a
surface.
• As you increase the
movement of the
particles, the pressure
increases.
• The unit of pressure is a pascal (Pa)
Pascal's Principle
• Pressure is transmitted undiminished or
unchanged throughout an enclosed static
fluid.
If the bottle is filled to the top
with water, then any pressure
exerted on the water is
transmitted undiminished to the
bottom of the bottle, which has
a larger area. The multiplied
force can pop the bottom out of
the bottle.
Bernoulli’s Principal
• States that as the velocity of a
fluid increases the pressure
exerted by the fluid decreases.
• Demonstration
Airplane Wing
• The air across the top of a
conventional airfoil
experiences constricted
flow lines and increased air
speed relative to the wing.
This causes a decrease in
pressure on the top according to
the Bernoulli equation and
provides a lift force.
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