Transcript Temperature & Heat

Temperature and Heat
Heat
Temperature
Internal Energy
Measurement of Heat
Specific Heat
Thermal Expansion
Temperature & Heat
• Absolute Zero Video – Nova
• Heat Mixes Lab
• Antifreeze in the Summer Lab
Temperature
• The quantity that tells how hot or cold
something is compared with a standard.
Temperature
• Temperature is a
measure of the average
kinetic energy of the
molecules of a
substance.
• A thermometer
measures this KE as
the molecules collide
with the
thermometer’s bulb.
Temperature Scales
Freezing point to boiling point of water
• Fahrenheit: 32 to
212, range of 180
degrees.
• Celsius: 0 to 100,
range of 100 degrees.
• Kelvin: 273 to 373,
range of 100 degrees.
Kelvin Scale
• At constant pressure the volume of a gas changes by
1/273 of its volume at 0Co with each 1Co change in
temperature.
• At -273 0Co the gas is reduced to 273/273 and the
volume is 0.
Heat
Some two hundred years ago heat was thought to be an
invisible fluid called caloric, which flowed like water from
hot objects to cold objects. Caloric appeared to be conserved –
that is, it seemed to flow from one place to another without
being created or destroyed. This idea was the forerunner of the
law of conservation of energy.
Heat is Kinetic Energy
• During the French Revolution Count Von Rumford
(Benjamin Thompson) was boring cannons for the
Bavarian army and he notice:
“I perceived, by putting my hand into the water and
touching the outside of the cylinder that, Heat was
generated; … at 2 hours and 30 minutes it (the water)
ACTUALLY BOILED…without any fire.”
• The generation of heat was related to the kinetic energy
of truing the cannon barrel.
Heat
Heat is the net energy transferred from one object to
another because of a temperature difference.
Internal Energy Includes:
• molecular translation
form place to place,
• molecular vibration,
• molecular rotate.
Heat versus temperature
Temperature
• A measure of hotness or
coldness of an object
• Based on average molecular
kinetic energy
Heat
• Based on total internal
energy of molecules
• Doubling amount at same
temperature doubles heat
Thermal Equilibrium
• When object on
contact with each
other reach the same
temperature and heat
no longer flows
between them.
How do we measure temperature?
Think about using a
thermometer
How does the thermometer know how
hot the substance is?
The molecules of the substance
bump into the thermometer and
transfer energy. How often and
how hard they bump into the
thermometer are directly related to
their speed. Temperature turns out
to be related to the average speed
of the molecules in a substance.
Temperature is not a measure of
the total amount of energy in an
object.
Thermal Energy = internal energy = a
measure of the total kinetic and
potential energy in an object
Measurement of Heat
• Heat is energy and thus has units of Joules.
• However, heat has a special unit of calorie.
• A calorie is the heat needed to raise one
gram of water by 1Co.
• 1cal = 4.186J
• 1kcal = 1000 cals
• 1Cal (food calorie) = 1000 cals
Specific Heat
• Each substance has its own specific heat.
• The specific heat of any substance is the amount
of heat it takes to raise 1kg of the substance by
1Co.
• Specific heat of water = 1.000 kcal/kgCo.
• H = mcDT, Where:
m = mass
c = specific heat
DT = change in temperature.
Specific Heat Table
Thermal Expansion
• Why?
• The Bridge Connection Lab
• Concept Development - Thermal Expansion
Thermal Expansion
Thermal Expansion
Thermal Expansion
•
•
•
•
Bimetallic Strip
Ball and ring
Drinking Bird
Soda Can (Yes, I can make it work!)
Expansion of Water
• This is a good thing.
• Water temp. vs. depth.
Yeah! Chapter Problems.
• Chapter 21: 2, 4, 5, 9, 10, 12, 13, 14, 15, 17,
19, 20, 23, 26, 28, 30, 31, 33 & 34.
Heat Transfer
• Conduction
• Convection
• Radiation
• Absorption of Radiant Energy
• Emission of Radiant Energy
• Newton’s Law of Cooling
• Global Warming / Greenhouse Effect
Solar Equality Lab
• Purpose: To determine the power output of
the sun.
Heat Transfer
Three mechanisms for heat
transfer due to a
temperature difference
1. Conduction
2. Convection
3. Radiation
Natural flow is always from
higher temperature
regions to cooler ones
Conduction
• Conduction –
• Conductor –
• Insulator
Conduction
• Heat flowing through
matter
• Mechanism
– Hotter atoms collide
with cooler ones,
transferring some of
their energy
– Direct physical contact
required; cannot occur
in a vacuum
• Poor conductors =
insulators (Styrofoam,
wool, air…)
Sample conductivities
Material
Relative conductivity
Silver
0.97
Iron
0.11
Water
1.3x10-3
Styrofoam
1.0x10-4
Air
6.0x10-5
Vacuum
0
Convection
• Convection -
Convection
• Energy transfer through
the bulk motion of hot
material
• Examples
– Space heater
– Gas furnace (forced)
• Natural convection
mechanism - “hot air
rises”
Heat Transfer
Convection in a House
Heat Transfer
The Wind
Sea Breeze
Land Breeze
Convection
• Why does rising warm air cool?
Heat Transfer
Convection on the Sun
Heat Transfer
Thermos Bottle
Radiation
• Radiation
Radiation
• Radiant energy - energy associated with
electromagnetic waves
• Can operate through a vacuum
• All objects emit and absorb radiation
• Temperature determines
– Emission rate
– Intensity of emitted light
– Type of radiation given off
• Temperature determined by balance between rates
of emission and absorption
– Example: Global warming
Radiation
• Absorption of Radiant Energy –
• Emission of Radiant Energy –
• Con. Dev. 22-1 Transmission of Heat
Solar Energy Lab 56
Newton’s Law of Cooling
Global Warming
• What causes it?
Greenhouse Effect
Video
• An Inconvenient Truth
Yeah! More Problems
• Chapter 22: 1, 2, 3, 4, 7, 8, 9, 12, 16, 17, 19,
20, 21, 22, 24, 25, 26, 27 & 28.
Chapter 24
Thermodynamics:
Laws of Thermodynamics Song:
http://www.youtube.com/watch?v=KTHiIwxcexI
Thermodynamics
• The study of heat and
its relationship to
mechanical and other
forms of energy
• Thermodynamic
analysis includes
– System
– Surroundings (everything
else)
– Internal energy (the total
internal potential and
kinetic energy of the
object in question)
• Energy conversion
– Friction - converts
mechanical energy into
heat
– Heat engines - devices
converting heat into
mechanical energy
– Other applications: heat
pumps, refrigerators,
organisms, hurricanes,
stars, black holes, …,
virtually any system with
energy inputs and
outputs
Absolute Zero
• Define:
• Compared to Celsius:
Lab
• The Uncommon Cold - #63
Kinetic Theory & Gas Laws
Temperature & Volume
Charles’ Law
Jacques Charles (1746-1823)
• The volume of a
fixed amount of
gas at constant
pressure is directly
proportional to its
absolute (Kelvin)
temperature.
• V = kT
http://www.grc.nasa.gov/WWW/K-12/airplane/aglussac.html
st
1
Law of Thermodynamics
• Define
• Heat added =
The first law of
thermodynamics
• Conservation of energy
• Components
– Internal energy
– Heat
– Work
• Stated in terms of
changes in internal
energy
• Application: heat
engines
Adiabatic Process
• Define:
Adiabatic Process
• Piston in engines:
nd
2
Law of Thermodynamics
• Define:
The second law of
thermodynamics
Equivalent statements:
•
No process can solely convert a quantity of heat
to work (heat engines)
•
Heat never flows spontaneously from a cold object
to a hot object (refrigerators)
•
Natural processes tend toward a greater state of
disorder (entropy)
Heat Engines
Definition:
Heat Engines
Carnot (ideal) Efficiency
• Ideal Efficiency =
• Example:
Order Tends to Disorder
• Entropy:
•
http://www.youtube.com/watch?v=5KIhDVLbMeY&feature=related
Entropy
• Things:
• Living systems:
• Useful energy:
More physics fun
• Chapter 24 # 1, 3, 4, 6, 11, 12, 31, 32 &
33.
• Chapter 24 # 13, 19, 21, 22, 23, 24, 37,
39 & 40.
Second law, third statement
• Real process =
irreversible process
• Measure of disorder =
entropy
Second law, in these terms:
• The total entropy of the
Universe continually
increases
• Natural processes
degrade coherent, useful
energy
– Available energy of the
Universe diminishing
– Eventually: “heat
death” of the Universe
• Direction of natural
processes
– Toward more disorder
– Spilled milk will never
“unspill” back into the
glass!
Kinetic Theory & Gas Laws
Pressure & Number of Molecules
• Pressure is directly
proportional to the
number of gases
molecules present.
• paN
Kinetic Theory & Gas Laws
Pressure & Temperature
• At constant volume
pressure is directly
proportional to the
Kelvin temperature.
• paT
Kinetic Theory & Gas Laws
Pressure & Temperature
A boiler explosion broke this locomotive into small pieces
and sprayed them, and the crew, over a wide area of Florida.
http://afu.com/steam/
Since we Mentioned Steam Engines
Thomas and his prototype
Kinetic Theory & Gas Laws
Pressure & Volume
Boyle’s Law
Robert Boyle (1627 – 1691)
• At constant
temperature pressure
is inversely
proportional to the
volume.
• p a 1/V where V =
volume.
http://www.grc.nasa.gov/WWW/K-12/airplane/aboyle.html
Kinetic Theory & Gas Laws
Ideal Gas Law
• Putting all three of these together the Ideal
Gas Law is obtained.
• P a (NT)/V
• The proportionally can be used to take
ratios for calculations.
• p2/p1 = (V1/V2)(T2/T1) assuming a constant
number of molecules, N.
Kinetic Theory and Atoms
John Dalton (1766 – 1844)
• All matter is composed of tiny particles.
• All atoms of each element are identical (he didn’t
know about isotopes.)
• Atoms are not created or destroy in chemical
reactions (conservation of matter.)
• Elements bond in whole ratios to form
compounds.
• Chemical reactions are the union and separation of
atoms.
Energy, heat, and molecular
theory
Two responses of matter
to heat
1. Temperature increase
within a given phase
–
–
Heat goes mostly into
internal kinetic energy
Specific heat
2. Phase change at
constant temperature
–
–
Related to changes in
internal potential energy
Latent heat
Phase changes
Solid/liquid
Liquid/gas
Solid/gas
Fusion
Vaporization
Sublimation
Temperature Melting point Boiling point
(Direction ->)
Sublimation
Latent heat
Temperature Freezing
(Direction <-) point
Condensation Sublimation
point
Evaporation and condensation
• Individual molecules
can change phase any
time
• Evaporation:
– Energy required to
overcome phase
cohesion
– Higher energy molecules
near the surface can then
escape
• Condensation:
– Gas molecules near the
surface lose KE to liquid
molecules and merge
Phases of Matter
Solid
• Molecules arranged in
a rigid crystalline
structure.
• Expansion occurs
during heating because
molecules vibrate with
grater amplitude.
Phases of Matter
Liquids
• Molecules not in a
lattice.
• Molecules can vibrate
and rotate.
• Molecules are still
close together.
• Take the shape of
container.
Phases of Matter
Gas
• Molecules relatively
far apart.
• Molecules have high
speed of Kinetic
Energy.
Latent Heat
•
•
•
•
•
Heat associated with a phase change.
Lf = latent heat of fusion
H = m Lf = heat needed to melt a substance.
Lv = latent heat of vaporization
H = m Lv = heat needed to vaporize a
substance.
Latent Heat
Latent heat of fusion used to break apart the
crystalline lattice of water.
Latent Heat Graph