Transcript Chapter02a

Energy, Temperature, Heat
Recap
• The
atmosphere may be divided into
layers (or regions) according to its
•
•
♦ vertical profile of temperature;
♦ gaseous composition;
♦ electrical properties.
We live at the bottom of the
troposphere, which is an atmospheric
layer where the air temperature
normally decreases with height, and
is a region that contains all of the
weather we are familiar with.
The study of the atmosphere and all
of its related phenomena is called
meteorology, a term whose origin
dates back to the days of Aristotle.
End of the chapter study material
• Key
terms: atmosphere, nitrogen, oxygen, water vapor, carbon
dioxide, ozone, ozone hole, aerosol, pollutants and acid rain
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(Chapter 18), outgassing, density, pressure, air pressure, lapse rate
(6), temperature inversion (3), troposphere, radiosonde,
stratosphere, tropopause, mesosphere, thermosphere, exosphere,
homosphere, heterosphere, ionosphere, weather, climate,
meteorology, middle latitudes and middle latitude cyclonic storm
(12), hurricane (15), thunderstorms and tornadoes (14), wind (8),
wind direction (9), front (11)
♦ Must learn now
♦ Will discuss later (in Chapter xyz)
Questions for review
Questions for thought
Problems and exercises
Questions for exploration
• Energy:
•
Energy and Work
♦ Definition: The ability or the
capacity to do work on some
form of matter
♦ Units: J (Joule), cal, erg
Work:
♦ Work is done when a body with
a non-zero mass is moved
(horizontally or vertically) over
a distance as a result of an
acting force.
♦ Units: same as energy, usually J
What is NOT work???
Kinetic/Potential Energy
• Kinetic Energy: E (J)
k
♦ Any moving object has a
kinetic energy
♦ High velocity = large Ek
♦ Large mass = large Ek
♦ Fast winds closer to the
ground correspond to
bigger Ek. (Why?)
• Potential Energy: E (J)
p
♦ The potential to do work.
Gravitational energy
(height)
Elastic energy
(deformation)
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•
1 2
E K  mv
2
H
E p  mgH
Energy can produce electricity
• Gravitational potential energy: hydropowerplants
• Kinetic energy: wind turbines, tidal harnesses
• Radiant (solar) energy: solar panels
• Chemical energy: batteries
• Nuclear energy: nuclear powerplants
• Heat: steam engines
Conservation of Energy
• Energy conservation law:
♦ The total energy of a closed system
remains constant.
♦ Energy cannot be created nor can it be
destroyed!
♦ Energy can only change from one form to
another, e.g. kinetic to potential and vice
versa.
• Mechanical system:
♦ The loss of Ek in a given process equals
the gain in Ep in the same process!
♦ The work is done by gravity or elastic
forces.
Radiant Energy
• The
energy emitted from the Sun is radiant energy. It is the
most important source of energy for the Earth’s atmosphere.
• Every body emits radiant energy (electromagnetic emission).
♦ Infrared, Visible, ultraviolet, X-rays, …
Thermal Energy and Temperature
• Definition:
E is kinetic energy
on a microscopic (molecular)
level.
• The
temperature is
proportional to the average
molecular kinetic energy.
• The
temperature is a measure
of the thermal energy.
T
ET  T
• The Absolute ZERO!
♦ No thermal energy.
♦ The atoms do not move.
♦ The absolute zero
practically cannot be
achieved.
1 2
E K  mv
2
Temperature Scales
• Kelvin (absolute scale) K
•
•
♦ No negative values
♦ Starts with THE O!
♦ Used in science
♦ Freezing point 273K
♦ Boiling point 373K
Fahrenheit
F
♦ Freezing point 32F
♦ Boiling point
212F
♦ 180 intervals
Celsius (Centigrade) C
♦ Freezing point 0C
♦ Boiling point 100C
♦ 100 intervals
Scale conversions
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• Fahrenheit -> Kelvin
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Kelvin
-> Celsius
K - 273
=C
Celsius
-> Kelvin
C + 273
=K
Fahrenheit -> Celsius
(F-32) x 5/9 = C
Celsius
Cx9/5+32
Kelvin
-> Fahrenheit
-> Fahrenheit
???
???
=F
Heat: Q
• from one object to another.
Heat is energy in the process of being transferred
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•
The amount of heat is equal to the change of energy
that results from the process of energy transfer.
Processes of heat transfer:
♦ Conduction;
♦ Convection;
♦ Radiation.
Heat Capacity
• Heat
capacity: the amount of heat energy that is required to
change the temperature of a body by 1 K.
♦ Heat capacity= Heat energy/Temperature change
Q
C
T
•
>
>
♦ It depends on the material and on the mass of the body
Specific heat capacity: the amount of energy that is required to
change the temperature of 1 gram of substance by 1 degree C.
Q
C
m T
=
♦ It does not depend on the mass of the body.
♦ It depends only on the material of the body.
>
Table 2-1, p. 30
Thermal inertia
• Bodies
with a large heat
capacity cool and/or heat up
very slowly.
♦ Analogy with a heavy body
(a big truck)
♦ Water has a high heat
capacity (large thermal
inertia) 1cal/gram/degree
♦ Regions near large bodies
of water (rivers, lakes,
oceans) do not experience
sharp temperature changes.
Their climate is mild.
♦ Air and land have smaller
specific heats than water.
Figure 3.23
Phase Changes
Phase transitions
(1 gram of water)
Sensible heat
600 cal
100C
Temperature C
Latent heat
100 cal
80 cal
0C
ICE
melting
water
HEAT IN
boiling
vapor
Latent heat
• Latent
heat: the heat required to
change a substance from one state
to another (phase change)
♦ Evaporation/Melting (cools the
environment)
♦ Condensation/Freezing (heats
the environment)
The importance
of latent heat