Transcript Document

Thermal Physics
3 key terms
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Heat – Energy in transit. The energy
transferred between objects because of a
difference in temperature.
Temperature – A measure of the average
Kinetic Energy of the particles in a substance.
Internal Energy – The energy of a substance
due to the random motions of its component
particles and the equal to the total energy of
those particles.
Temperature
 We
often associate temperature
with how hot or cold something
feels
 Hot and Cold are terms that can be
misleading
 The same object can feel warm or
cool depending on the properties of
the object and the condition of your
body
Hot
Cold
Luke warm
Moving Energy
Changes Temp. Heat
 Consider
an oven- turn the
dial on and heat is
delivered as energy flows.
When the dial is off, energy
stops flowing and
temperature cools
Temperature
Temperature is proportional to the
Kinetic Energy of atoms and molecules.
 To understand temperature, think of
atoms & molecules and how they move.
With more heat, atoms move more, have
more KE. When heat is removed, the
energy of theses moving atoms/
molecules is called internal energy.
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Internal Energy
 The
energy of substance
due to the random motions
of its component particles
and equal to the total
energy of those particles
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Why does a 1200oC sparkle not hurt you, but a
200oC stove burner will give you a nasty burn?
A plasma torch in a welding shop has
temperatures hotter than the Sun’s surface,
why aren’t welders vaporized?
What has more energy; a cup of boiling hot
water or Lake Conroe in the winter time?
Thermal Equilibrium
 The
state in which two bodies in
physical contact with each other
have identical temperatures
In time both liquids
Warm
will have equal
Beverage
temperatures
COLD
WATER
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You can not find temperature until thermal
equilibrium is reached
The temperature of the liquid in the
thermometer must balance the
temperature of the object being
measured. This must happen in order to
know the temperature
“You don’t read a thermometer until the
mercury/ alcohol has stopped rising/
falling”
Thermal Expansion
Things get HOT they EXPAND
 Things get COLD they CONTRACT
– Concrete bridges
– Rail Road Rails
– Power Lines
– Hot glass – cold water – cracks
 This is True for all solids, liquids and
gasses (some more than others)
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Anomaly of Water
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A strange thing happens
to water between
0°- 4°C: as it gets colder,
it EXPANDS- GOOD NEWS FOR FISH!!
ICE 0°C
1°
2°
3°
4°
Thermometers
A
glass tube containing a thin
column of mercury, colored
alcohol, or colored mineral
spirits
 When heated, Liquid Expands
Calibrating Thermometers
 To
calibrate thermometers
and to set a standard for
temperature we have chosen
water to be our bench mark.Not just any water – Pure
Water at 1ATM of Pressure
What About
Fahrenheit?
 We
must convert with the
following formulas:
– To find °F
°F = (9/5(°C)) + 32
–
To Find °C
°C = 5/9(°F - 32)
Kelvin Scale
With °F and °C, often times you get
negative numbers; This is because
many things are colder than our
standard “ice”
 To eliminate neg. values for
temperature, the Kelvin Scale was used
– 0 Kelvin is as cold as anything can get
– From 0 K, you can only go up
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Kelvin Scale
 The
best thermal lab on
record has reached
0.0000001 K
 At 0K, the theory states that
atoms would cease to vibrate,
liquids would contract no
more.
Kelvin Conversions
 To
find K
Kelvin temp = °C + 273.15
 To find °C
°C = Kelvin Temp - 273.15
Practice Problems 10A 1-5 pg 363
HOMEWORK 2, 4, 5, 7, 9, 10 pg.387
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A piece of iron has a temperature of 100C. A
second identical piece of iron in twice as hot.
What is the temperature of the second piece of
iron?
10+273=283K
283x2 = 566K
566 – 273 =
293oC
Section 10-2
Defining Heat
Read
and
Understand
p. 365-367
Defining Heat
Heat:
–
–
–
–
Flow of energy
Moves in one direction, from hot to
cold
Symbol Q
Has units for energy (Joule)
(calorie, kilocalorie, dietary calorie,
Btu, therm)
Mechanical Energy is Equal to
Heat Energy
KE=PE=work=Q=heat
Doing work on a substance
will cause it to heat up.
Specific Heat Capacity
This is the amount of energy required to
change the temperature of 1kg of a
substance by 1 °C
Cp = Q/ mΔT
Q = m CP ΔT
Q = Heat (Joules)
m = mass (Kg)
Cp = Specific Heat (J/Kg°C)
ΔT = change in temp (°C)
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Table 10.4 pg 372
 Substances
take differing
amounts of energy to heat
up
– Water heats up Slowly
– Lead heats up fast
Calorimetry
 To
determine specific heat capacity
we do calorimetry
 For calorimetry always remember:
Energy absorbed = Energy released
Qwater = Qx
CPw Mw ΔTw = Cpx Mx ΔTx
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Q T graphs
Heat Temperature Graphs
Heat Flow
Thermal Conduction: this is how heat
flows through a substance. Some
materials conduct heat well. others are
very poor (insulators)
 Generally, metals are good conductors
of heat. Asbestos, cork, ceramic,
cardboard,& fiberglass are good
insulators
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Heat Moves in 3 Ways
Conduction: heat moving through 2
objects that touch each other
 Convection: heating by movement of
fluids(liquids and gases). Involves
displacement of cold matter by hot
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Heat Movement Cont…
 Radiation:
electromagnetic rays
carry heat from everything above
0 Kelvin in the form of waves. No
medium is needed for thisoccurs in the vacuum of space.
Also, near a campfire
Thermos
 Keeps
hot things hot, cold
things cold because it
minimizes heat flow
OVERHEAD
Clothes & climate
Eskimo- Parka
– Arabian - Desert Dress
–
Laws of Thermodynamics
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Heat, Work, and Internal Energy
Q is heat, W is Work, U is internal Energy
System- A collection of matter within a clearly
defined boundary across which no matter
passes.
Environment- Everything outside a system that
can affect or be affected by the system’s
behavior.
Defining Work in terms of Changing
Volume
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W = Fd
Work = force x distance moved
p.404 insert formula proof
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Work = pressure x volume change
Pressure
p. 405 11A
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1 and 2
1. A) 6.4x105 J
B) -4.8x105 J
2. -167.5 J; Work is done on the
gas because the volume change
is negative
First Law of Thermodynamics
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This law is a statement of the Law of Conservation of
Energy.
Heat, Work, and the Change in Internal Energy can be
calculated.
U=Q–W
U-change in internal Energy
Q-energy transferred to or from a system as heat
W-Energy transferred to or from a system as work
Page 409
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Look at the roller coaster and the bar graphs
below to see an example of this view of the
Conservation of Energy.
Page 413 11B problems 1-3
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33J
-143 J; removed as heat
10,000J
Second Law of Thermodynamics
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The Universe and all systems are moving
towards greater disorder.
The Entropy of the Universe increases in all
natural processes.
Heat and entropy are related.
Entropy increases because energy is
transferred as heat to a system.
Entropy
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Entropy is a measure of a system’s disorder.
Increasing disorder reduces the energy
available for work.
Greater disorder means there is less energy to
do work.
Direction of Energy
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Always towards a state of disorganization
In order to organize energy, more energy must
be input.
Clean room
Salt pepper shaker
Heat death of the Universe.
T
Q
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