Chapter 6 Notes

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Transcript Chapter 6 Notes

Temperature – the measure of the average
kinetic energy of the particles in an object
◦ What is kinetic energy?
◦ So what does that tell you about the particles?
All matter is made of tiny particles
The particles are always in constant, random
motion moving in all directions at different
The faster they move, the more kinetic energy
they have
Particles move faster in hot objects than in cooler
( Figure 1 p. 158 and Q p.159)
As temperature INCREASES, the average
speed of the particles in random motion
Ex) The temperature in hot tea has a higher
temperature of iced tea because the particles
are moving faster on average
SI unit for temperature = K (Kelvin)
◦ You can also use Celsius
8.2 Temperature
 There are two common
temperature scales.
 On the Fahrenheit scale,
water freezes at 32
degrees and boils at 212
 The Celsius scale divides
the interval between the
freezing and boiling
points of water into 100
8.2 What temperature really is
 Atoms are in constant
motion, even in a solid
 The back-and-forth
jiggling of atoms is
caused by thermal
energy, which is a kind
of kinetic energy.
8.2 What temperature really is
 Temperature measures the kinetic
energy per molecule due to random
8.2 Thermometers
 A thermometer is an instrument
that measures the exact
 Most thermometers contain either a
silvery fluid (mercury) or a red fluid,
which is alcohol containing a small
amount of red dye.
8.2 How a thermometer works
The volume of alcohol in a
thermometer contains huge
numbers of alcohol
As temperature increases, the
alcohol molecules move
faster and bounce off each
The liquid alcohol expands
and takes up more space in
the thermometer.
8.2 Measuring temperature
A thermistor is a device that
changes its electrical
resistance as the temperature
Some digital thermometers
sense temperature by
measuring the resistance of
electrons passing through
8.2 Liquid-crystal thermometers
Some thermometers contain liquid crystals that
change color based on temperature.
As temperature increases, the molecules of the liquid
crystal bump into each other more and more.
This causes a change in the structure of the crystals,
which in turn affects their color.
8.2 Absolute zero
 Absolute zero is -273°C.
 You cannot have a temperature lower than
absolute zero.
 Think of absolute zero as the temperature at
which atoms are “frozen.”
8.2 Converting to Kelvin
 The Kelvin
temperature scale is
useful in science
because it starts at
absolute zero.
 To convert from
Celsius to Kelvin,
you add 273 to the
temperature in
Energy – the sum of the kinetic and
potential energy of all the particles in an object
(total energy of particles)
◦ Thermal energy increases as temperature increases
◦ Thermal Energy is also called ____________.
When temp increases, KE increases
Mass also affects thermal energy…if the
temperature does not change, the thermal
energy in an object increases if the mass of
the object increases (more particles = more
KE = higher temp)
Unit: Joules
Heat - Thermal energy that flows from
something at a higher temperature to
something at a lower temp
Unit: Joules ( J) (it is a form of energy)
Heat always flows from warmer to cooler
Ex) Can you tell if someone has been sitting
in your chair? How and why?
Specific Heat – the amount of heat needed to
raise the temperature of 1kg by 1 degree Celsius
◦ As a substance absorbs heat (like the ocean at the
beach), its temperature change depends on the nature
of the substance AND the amount of heat added
Measured in J/(kg degree C)
◦ Compared to other materials, water has the highest
specific heat
◦ Water can absorb heat without a large change in temp
◦ That makes it useful as a coolant
◦ EX) That is how it is used in automobile engines (if
water temp is lower than the engine temp, heat will flow
from the engine to the water)
 FIGURE 4 p.161 and Specific heat Discussion Q
Measuring Specific Heat
Calorimeter – measures using the mass,
change in temp, and amount of heat
absorbed or released
A. Celsius
B. Fahrenheit
C. Kelvin
D. Joules
Cold to hot
Warm to hot
Hot to cold
Heat does not travel
A. Vibrate
B. Vibrate slowly
C. Do not move
D. They do not collide
Slow down
Are overheated
B. Reach supreme zero
C. Reach absolute zero
D. Are frozen
Transfer of thermal energy by collisions and
vibrations between particles in matter
 Occurs because particles are in constant motion
◦ Ex) If a spoon is heated by a flame on a Bunsen burner,
what happens?
 Kinetic Energy of the Particles near the heat source (flame)
 These particles collide with neighboring particles,
transferring kinetic energy
 The KE gets transferred from one end of the spoon to
 Thermal energy gets transferred without changing or
moving matter
All materials can be conductors, but the heat
moves differently in different objects
 Heat conducts faster in solids and liquids than in gases
 (Heat in gases moves more slowly because the particles are
farther apart, therefore there are fewer collisions)
 Best Conductors are Metals (more freely moving electrons)
Convection – transfer of thermal energy in fluids by
the movement of warmer and cooler fluid from
place to place (gases and liquids)
Particles with a lot of energy collide with particles
with less energy and transfer thermal energy
The faster particles move, the more they spread
◦ Therefore, fluid expands as temperature increases
Convection Currents – rising and sinking action that
causes a transfer heat from warmer to cooler parts
of the fluid – in both conduction and convection
Deserts and Rain Forests
atmosphere is made up of gases
Atmosphere is warmer at equator than at poles
Warmer on surface than at higher altitudes
The temperature differences create convection currents
 P. 166 Visualizing Convection Currents
How the sun’s heat travels through space
Little matter exists in space between Sun and
Earth, so heat must be transferred through
Radiation – transfer of energy by electromagnetic
waves (which can travel through space even
when no matter is present)
This energy is often called Radiant Energy
Ex) When you warm your hands by a fire
Ex) Sun
When radiation strikes a material, some of the
energy is absorbed, some is reflected and some
may be transmitted through the material
The amount of energy is determined by the type
of material.
◦ Light colored materials reflect more
◦ Dark colored absorb more radiant energy
B. Conduction
C. Radiation
Outer core
Inner core
Heat falls and cold rises
Heat rises and cold falls
Heat and cold do not
The plastic popsicle stick
The metal bowl
The air around the flame
They will conduct heat the same
With a shoulder partner, come up with 2
examples of Conduction, Convection and
Everyday examples:
◦ wearing a coat when it is cold outside
◦ using a cloth or pot handle to lift hot dishes out of the
 In these examples, you used materials to control the flow
of heat
Almost all living things have special features
that help control the flow of heat
◦ Seal’s thick coat (keeps it from losing heat)
◦ Emperor penguins thick layer of blubber
◦ Thin, scaly skin of desert lizard (reflects sun’s rays)
A material in which heat flows slowly (poor
◦ Wood, wool, fiberglass, some plastics, air
◦ Metals and other conductors of heat are poor insulators
Gases, like air, are usually better insulators (air
pockets heat poorly and keep convection
currents from flowing)
◦ Fleece jackets work the same way – fleece fibers trap
and hold air next to you, which prevents the flow of
heat from your body
Insulating buildings – protect from weather,
keeps furnaces and ACs working efficiently,
saving energy
Why are good conductors of heat poor
Predict whether plastic foam, which contains
pockets of air, would be a good conductor or
insulator. Explain.
Critical Thinking Question
Several days after a snowstorm, the roofs of
some homes on a street have almost no snow
on them, while the roofs of other homes are
still snow-covered. Describe what would
cause this difference.
If a cup of coffee and a red popsicle were left
on the table in this room what would happen
to them? Why?
Why does hot air rise and cold air sink?