Transcript Chapter 13

Chapter 13
States of Matter
By: Zak and Megan
13.1 The Fluid States
Properties of Fluids
• Fluids include both liquids and gases
– Fluids are materials that flow and have no
definite shape
– Liquids have definite upper surface area
– Gases do not have any definite surface area
• Applying force to a surface is pressure
– Pressure is the force on a surface divided by the
area of the surface.
F
–P= A
• The force (F) is perpendicular the surface area (A).
– The unit for pressure is the pascal (Pa).
• More commonly used is the kilopascal (kPa)
– Pressure is exerted up from a solid surface
equal to the weight of the object resting on it.
Gas Particles and Pressure
• The kinetic molecular theory of gases states that
gases are made up of very small particles that are
widely separated in constant, random motion at
high speed, and making elastic collisions with
each other.
– Gas particles “bounce” off a surface without losing
kinetic energy and these collisions result in gas pressure
on the surface.
• Atmospheric Pressure exerts approx 10N of force
on every cm2 of Earth’s surface.
– Patm = 10 N/cm2 or 100 kPa
Example Problem
A woman weighs 495 N and wears shoes that touch the ground over an area
of 412 cm2.
a. What is the average pressure in kPa that her shoes exert on the
ground?
b. How does the pressure change when she stands on only one foot?
c. What is the pressure if she puts all her weight on the heel of one shoe
with the area of the high heel of 2.0 cm2.
Known:
F = 495 N
Aa = 412 cm2
Ab = 206 cm2
Ac = 2.0 cm2
Ex. Problem Cont.
Calculations:
a. Aa 412 cm2 (1 m/100 cm)2 = 0.0412 m2
Pa = 495 N/ 0.0412 m2 = 1.20 x 104 N/m2 (1 kPa/1000 N/m2 ) = 12.0
kPa
b. Ab = 0.0206 m2
Pb = 495/(.0206 x 1000) = 24.0 kPa
c. Ac = .00020 m2
Pc = 495/(.00020 x 1000) = 2500 kPa
Fluids at Rest
• Pascal's Principal states that any change of pressure
applied at any point on a confined fluid is
transmitted undiminished throughout the fluid.
Swimming Under Pressure
• The downward pressure of the water is equal to the
weight (Fg) of the column of water above its surface
area.
– Fg = rAhg
• r = density
– P = rgh
SUP Cont.
• The upward force on an object in water is called the
buoyant force.
– Fbuoyant = Fbottom – Ftop
– Fbuoyant = rVg
• Archimedes' principle states that an object
immersed in a fluid has an upward force on it equal
to the weight of the fluid displaced by the object.
• The net downward force of an object is its apparent
weight.
Fapparent = Fg – Fbuoyant
Fluids In Motion
•
•
The relationship between the velocity and
pressure exerted by a moving fluid is described
by Bernoulli's Principle.
– As the velocity of a fluid increases, the
pressure exerted by that fluid decreases.
As a fluid moves through a narrower area the
velocity of the fluid increases.
Forces Within Liquids
•
•
In real liquids particles exert electromagnetic
forces of attraction on each other called cohesive
forces.
– Surface tension is a result of cohesive
forces between the particles of a liquid.
Adhesion is the attractive force that acts between
particles of different substances.
– Capillary action is when a liquid moves up
a tube because its adhesive forces are
stronger than the cohesive forces.
Forces Within Liquids
•
The escape of particles from a liquid is
called evaporation.
–
–
•
Evaporation has a cooling effect.
A liquid that evaporates quickly is called a
volatile liquid.
The returning of evaporated particles to a
liquid is called condensation.
13.2 The Solid State
Solid Bodies
• When the temperature of a liquid is lowered to the
point where the particles can no longer move past
each other, the particles lock into a pattern called a
crystal lattice and form a crystalline solid.
– The solids still vibrate.
• Some solids do not form a fixed crystal lattice and
are called amorphous solids.
– Known as being viscous, or slowly
flowing, liquids.
Effects Of Freezing
•
•
Solids are usually more dense than liquids
(except water).
An increase in pressure on the surface of a liquid
usually increases its freezing point (except
water).
Elasticity
•
The ability of an object to return to its original
form when bent or twisted is called the elasticity
of the solid.
– The elasticity limit is the point a solid is
deformed to the point that it will not return.
Thermal Expansion
•
•
•
•
Temperature changes in both solid and liquid
matter causes it to expand when heated and to
contract when cooled (thermal expansion).
When heated matter becomes less dense and fills
more space.
The change in length of a solid is propotional to
the change in temperature.
Liquids expand considerably more than solids.
Plasma
•
•
•
If the temperature of a gas is increased enough,
the particles of the substance start to tear apart
into negative electrons and the positive ions. The
resulting state is called plasma.
Most of the matter in the universe is plasma.
– Stars consist mostly of plasma.
– Much of space consists of hydrogen w/o
electrons.
The main difference between a gas and plasma is
that a plasma can conduct electricity.
– Lightning bolts are in the plasma state.
Practice
Pg. 303 # 1-4, Pg. 309 # 6