Transcript Unit 5 Matter Ch 18,19,20

Matter
Ch. 18 - 20
Phases of Matter
• Review… The four Phases of Matter are…
1.
2.
3.
4.
Solids
• Properties
1. Crystal Structure
2. Density
Solids
• Properties Cont…
3. Elastic Materials – Returns to original shape after
distortion. (Ex. Slinky)
•
Elastic Limit – Distance at which permanent distortion
occurs
4. Inelastic Materials – Do not resume original
shape after distortion. (Ex. Clay)
Solids
• For Elastic Materials…
– Hookes Law - the amount of stretch (or compression),
is directly proportional to the applied force. F ~ ∆x
Solids
• Compression and Tension
Between the top and bottom, there is a region that is neither
stretched nor compressed. This is the neutral layer.
Compression and Tension
• I-Beams
– An I-beam is like a solid
bar with some of the
steel scooped from its
middle where it is
needed least. The
beam is therefore
lighter for nearly the
same strength.
Scaling
• The study of how size affects the relationship
between weight, strength, and surface area.
An ant can carry the weight of several ants on its back, whereas a
strong elephant could not even carry one elephant on its back.
If an ant were scaled up to the size of an elephant, would it be
several times stronger than an elephant?
Scaling
• As the size of a thing increases, it grows
heavier much faster than it grows stronger.
• How scaling affects strength
– Weight depends on volume
– Strength comes from the area of the cross-section
of the limb. Ex’s. Tree limbs, animal limbs…
Scaling
• A 1-cm cube has a cross section of 1 cm2 and its
volume is 1 cm3.
• A 2-cm cube of the same material has a crosssectional area of 4 cm2 and a volume of 8 cm3.
• What about a 5-cm cube?
– Volume = ________
– Cross sectional area = __________
Scaling
How scaling affects strength.
• Compare the thick legs of large animals to
those of small animals: an elephant and a
deer, or a tarantula and a daddy longlegs.
Scaling
• Surface area to volume ratio
– Smaller objects have more surface area per
kilogram.
• Cooling occurs at the surface… So crushed ice cools a
drink faster than an ice cube! (The crushed ice
presents more surface area)
• Steel wool rusts faster than a solid piece of steel.
• Chunks of coal burn, while coal dust explodes!
• Thin French fries cook faster in oil than fat fries.
• Flat burgers cook faster than meatballs.
Scaling
• Scaling and living organisms
– The big ears of an elephant
are not for hearing, but for
cooling!
– If an elephant did not have
large ears, it would not have
enough surface area to cool
its huge mass.
Liquids
Liquids
• Liquid pressure depends on depth (not on
volume).
Soda Bottle Demo
Liquid Pressure
think!
A brick mason wishes to mark the back of a
building at the exact height of bricks already laid
at the front of the building. How can he measure
the same height using only a clear garden hose
and water?
Buoyancy
• Buoyancy: Apparent loss of weight of objects
when submerged in a liquid.
Buoyancy
• The upward forces against the bottom of a
submerged object are greater than the
downward forces against the top. There is a
net upward force, the buoyant force.
Bouyancy
• When an object is submerged, it displaces a
volume of water equal to the volume of the
object itself.
Archimedes Principle
• States… “the buoyant force on an immersed
object is equal to the weight of the fluid it
displaces”
The weight of the fluid displaced is = to the
buoyant force on the rock
Archimedes Principle
• A brick weighs less in water than it does in air.
Archimedes Principle
think!
A block is held suspended beneath
the water in the three positions, A,
B, and C. In which position is the
buoyant force on it greatest?
Answer:
The buoyant force is the same at all three
positions, because the amount of water
displaced is the same in A, B, and C.
Does It Sink, or Does It Float?
• Sinking and floating can be summed up in 3
simple rules.
– An object more dense than the fluid in which it is
immersed sinks.
– An object less dense than the fluid in which it is
immersed floats.
– An object with density equal to the density of the fluid in
which it is immersed neither sinks nor floats.
Does it Sink or Float?
• The wood floats
because it is less dense
than water.
• The rock sinks because
it is denser than water.
• The fish neither rises
nor sinks because it has
the same density as
water.
Flotation
• How does a ship made of iron float?
– Iron is nearly 8 times more dense than water
• The answer is in the shape of the hull!
Flotation
• The iron bowl still weighs 1 ton but if you lower the
bowl into a body of water, it displaces a greater
volume of water.
• The deeper the bowl is immersed, the more water is
displaced and the greater is the buoyant force
exerted on the bowl.
• When the weight of the displaced water equals the
weight of the bowl, it will sink no farther.
• The buoyant force now equals the weight of the
bowl.
Flotation
A solid iron block sinks, while the same block
shaped to displace more water floats.
Flotation
• Every ship must be
designed to displace a
weight of water equal to
its own weight.
• A 10,000-ton ship must
be built wide enough to
displace 10,000 tons of
water before it sinks too
deep below the surface.
Flotation
• The same ship is shown empty and loaded.
The weight of the ship’s load equals the
weight of extra water displaced.
Pascal’s Principle
• Describes how changes in a pressure are
transmitted in a fluid.
• The principle behind all hydraulic systems.
Pascal’s Principle
• A 1-N load on the left
piston will support 50N load on the right
piston.
• The piston on the left
has an area of 1cm2.
• The piston on the right
has an area of 50cm2.
Pascal’s Principle
• The automobile lift is
in many service
stations.
• Whatever air pressure
the compressor
supplies to the
reservoir, is
transmitted through
the oil to the piston
that raises the car.
Gases
Chapter 20
Atmospheric Pressure
• Caused by the weight of the air above us.
– When a Boeing 777 is fully pressurized
approximately 1000 kg is added to it’s mass.
Measuring Air Pressure
• An instrument used for measuring the
pressure of the atmosphere is called a
barometer.
– In a simple mercury barometer, a glass tube
(longer than 76 cm) closed at one end, is filled
with mercury and tipped upside down in a dish of
mercury.
– The mercury in the tube runs out of the
submerged open bottom until the level falls to
about 76 cm.
Air Pressure
• You cannot drink soda through the straw
unless the atmosphere exerts a pressure on
the surrounding liquid.
Measuring Air Pressure
• An aneroid barometer is an instrument that
measures variations in atmospheric pressure
without a liquid.
• Since atmospheric pressure decreases with
increasing altitude, a barometer can be used to
determine elevation.
Boyles Law
• “The product of pressure and volume for a
given mass of gas is a constant as long as the
temperature does not change”
Boyles Law
Describes the relationship between the pressure
and volume of a gas.
P1V1 = P2V2
P1 and V1 represent the original pressure and volume
P2 and V2 represent the second, or final, pressure
and volume
Boyles Law
think!
If you squeeze a balloon to one third its volume,
by how much will the pressure inside increase?
Bernoulli’s Principle
• In it’s simplest form states…
“when the speed of a fluid increases, pressure in the
fluid decreases”
Water flows through the pipe below.
Describe the velocity through the wide portion vs. the narrow portion.
How does this relate to pressure within the pipe?
Application of Bernoulli’s Principle
• In high winds, air pressure above a roof can
drastically decrease.
Application of Bernoulli’s Principle
• Throwing a curve ball.
Applications of Bernoulli’s Principle
• Passing Boats run the risk of a sideways
collision.
• Try this experiment in your sink!
Application of Bernoulli’s Principle
…the shape of an airplane’s wing!
• Due to the shape of airplane wings, air passes somewhat
faster over the top surface of the wing than beneath the
lower surface.
• Pressure above the wing is less than pressure below the wing.
• Lift is the upward force created by the difference between the
air pressure above and below the wing.