Thermal Energy

1
Thermal Energy

• Internal energy energy of the moving particles
  that compose matter

2
Starter 3 Thermal Energy Transfer

• Read Ch. 22.1-22.3
• Fold a piece of notebook paper to form three
  columns
• Head each column with one of the three ways that
  thermal energy can be transferred
• Define each
• List three main points from the reading for each
  thermal energy transfer process
• On the back of the paper, prepare an example
  illustrating how each transfers heat

3
Todays Key Terms and Ideas

• Thermal Energy
• Kinetic Theory
• Heat
• Thermal Equilibrium and heat transfer
• Kinetic Theory as it relates to expansion and
  contraction
• Hot vs. cold

4
Physics and Particles

• Particle is a general term used to describe
  molecules, atoms and sub-atomic particles

5
21.1 Temperature

• The higher the temperature of a substance, the
  faster the motion of its molecules.
• This is also referred to as the Kinetic Theory
• all matter is made of atoms and molecules that
  are moving.
• The higher the temperature, the faster the
  particles move.
• Given the same temperature, heavier particles
  move slower than lighter particles.

6
Matter is changing state
solid
Increasing Avg. KE Increasing Temp.
Particle speed is increasing
melting
freezing
liquid
evaporation
condensation
gas
7
21.1 Temperature

• Temperature and Kinetic Energy

Temperature is related to the average kinetic
energy of the atoms and molecules in a
substance. The faster the molecules move, the
______________ the temperature and the
_____________ the average kinetic energy and the
__________ the particle speed.
greater
greater
greater
8
21.2 Heat

1. Heat is the quantity of thermal energy
   transferred
2. Heat always flows from a substance with a higher
   temperature to a substance with a lower
   temperature.
3. Heat flows only when there is a difference in
   temperature.
4. Heat units are calories or joules.

9
hotter
21.2 Heat
Entropy! Flow from higher to lower energy state.
Just as water will not flow uphill by itself,
regardless of the relative amounts of water in
the reservoirs, heat will not flow from a cooler
substance into a hotter substance by itself.
colder
10
21.2 Heat
What causes heat to flow?
A difference in temperature between objects in
thermal contact.
11
21.4 Internal Energy

• When a substance takes in or gives off heat, its
  internal energy changes.

12
21.3 Thermal Equilibrium
What happens when a warmer substance comes in
contact with a cooler substance?

• Heat flows between two objects of different
  temperature until they have the same temperature.
  
• The loss of thermal energy from the warmer object
  equals the gain of thermal energy for the cooler
  object

13
21.8 Thermal Expansion

• Most forms of mattersolids, liquids, and
  gasesexpand when they are heated and contract
  when they are cooled.

14
21.8 Thermal Expansion

• When the temperature of a substance is increased,
  its molecules jiggle faster and normally tend to
  move farther apart.
• This results in an expansion of the substance.
• Gases generally expand or contract much more than
  liquids.
• Liquids generally expand or contract more than
  solids.

15
Starter Question 2How does a thermometer work?

• The kinetic theory be used to explain expansion
  and contraction of materials when the temperature
  of the material changes.
• As the temperature rises, heat is transferred
  from the surroundings to the liquid inside the
  thermometer and the molecules that compose the
  liquid vibrate faster. This causes the liquid to
  expand and rise.
• As the temperature falls, heat is transferred
  away from the liquid inside to the surroundings
  and the molecules that compose this liquid slow
  down. This causes the liquid to contract.

16

• The liquid in the thermometer stops rising or
  falling when thermal equilibrium is reached (no
  more heat flow!)

Air temperature Liquid temperature
17
21.6 Specific Heat Capacity

• Do copper, clay and water have the same chemical
  composition?
• No. Copper is composed of Cu atoms and water is
  composed of H2O molecules. Clay is a complex
  silicate.
• The difference in chemical composition influences
  how copper, clay and water respond when heat is
  transferred.

The specific heat capacity of a substance is the
quantity of heat required to raise 1 g of a
substance by 1 degree Celsius.
18
21.6 Specific Heat Capacity
A substance with a high specific heat capacity
can absorb a large quantity of heat before it
will raise in temperature (water has a high
specific heat). A substance with a low specific
heat requires relatively little heat to raise its
temperature (copper has a low specific heat).
19
21.6 Specific Heat Capacity
highest
lowest
20
21.6 Specific Heat Capacity

• think!
• Which has a higher specific heat capacitywater
  or sand? Explain.

21
21.6 Specific Heat Capacity

• think!
• Which has a higher specific heat capacitywater
  or sand? Explain.
• Answer
• Water has a greater heat capacity than sand.
  Water is much slower to warm in the hot sun and
  slower to cool at night. Sands low heat
  capacity, shown by how quickly it warms in the
  morning and how quickly it cools at night,
  affects local climates.

Good conductors have a low specific heat capacity!
22
21.6 Specific Heat Capacity
A gram of water requires 1 calorie of energy to
raise the temperature 1C. It takes only about
one eighth as much energy to raise the
temperature of a gram of iron by the same amount.
The capacity of a substance to store heat depends
on its chemical composition.
23
21.6 Specific Heat Capacity
24

• 6. What is the difference between a substance
  with a high specific heat and a low specific heat
  capacity?

25

• Substances with a low specific heat (e.g.,
  metals) need very little heat to raise
  temperature
• Good conductors, not good absorbers, do not hold
  onto heat well
• Substances with a high specific heat need a large
  quantity of heat to raise temperature.
• Poor conductors, good absorbers, store and hold
  onto heat well

26

• 7. How does the specific heat of water help to
  moderate climate?

27

• During the summer, surrounding air is cooled by
  the water and keeps the coast cooler than the
  intercontinental locations.
• During the winter, the surrounding air is warmed
  by the water and keeps the coast warmer than the
  intercontinental locations.

28
21.7 The High Specific Heat Capacity of Water

• The property of water to resist changes in
  temperature improves the climate in many places.

29
21.7 The High Specific Heat Capacity of Water
Water has a high specific heat and is
transparent, so it takes more energy to heat up
than land does.
30
21.7 The High Specific Heat Capacity of Water
Waters capacity to store heat affects the global
climate. Water stores and hold heat well because
of its high specific heat.

• Gulf Stream brings warm water northeast from the
  Caribbean.
• It holds much of its thermal energy long enough
  to reach the North Atlantic off the coast of
  Europe.
• As it cools, the energy released is carried by
  the prevailing westerly winds over the European
  continent.

31
The Gulf Stream brings warm winters to Ireland
and the prevailing winds off the Atlantic carry
with them rain. It means grass can grow almost
all year round creating the lush sweeping
pastures of the Emerald Isle. Today they make up
93 percent of all farmland. No other country in
Europe has quite as much grass as Ireland.
32
(No Transcript)
33
(No Transcript)
34
(No Transcript)
35
21.7 The High Specific Heat Capacity of Water

• Climate of Europe

Look at a world globe and notice the high
latitude of Europe. Both Europe and Canada get
about the same amount of the suns energy per
square kilometer.
36
Marine Climate
Continental Climate
Cork
Edmonton
Same insolation angle, different climate due to
proximity to water and the warming effect from
the Gulf Stream
http//www.sampleireland.com/weather-in-ireland-ye
ar-round.html
37
(No Transcript)
38
21.7 The High Specific Heat Capacity of Water

• Climate of America

• On the west coast, air moves from the Pacific
  Ocean to the land.
• In winter, the water warms the air that moves
  over it and warms the western coastal regions of
  North America.
• In summer, the water cools the air and the
  western coastal regions are cooled.

The central interior of a large continent usually
experiences extremes of temperature. Land, with
a lower specific heat capacity, gets hot in
summer but cools rapidly in winter.
39

• 8. In which three ways can the thermal energy (or
  heat) of a substance be transferred?

40

• Heat can be transferred by conduction, by
  convection, and by radiation.

41
22.1 Conduction

• In conduction, collisions between particles
  transfer thermal energy, without any overall
  transfer of matter.

42
22.1 Conduction
Heat from the flame causes atoms and free
electrons in the end of the metal to move faster
and jostle against others. The energy of
vibrating atoms increases along the length of the
rod.
43
22.2 Convection

• In convection, heat is transferred by movement of
  the hotter substance from one place to another.

44
22.2 Convection

• Convection occurs in all fluids.
• Convection currents transfer heat in air.

Hot, less dense fluid rises in the presence of
cooler, more dense fluid.
45
22.2 Convection

• Convection occurs in all fluids.
• Convection currents transfer heat in air.
• Convection currents transfer heat in liquid.

When fluid particles at the bottom of the pan
begin to vibrate faster, they expand and decrease
in density, making the hotter fluid more buoyant.
46
22.3 Radiation

• In radiation, heat is transmitted in the form of
  radiant energy, or electromagnetic waves.

47
22.3 Radiation
Most of the heat from a fireplace goes up the
chimney by convection. The heat that warms us
comes to us by radiation.
48

• Radiation is caused by moving electrons or
  charged particles in matter. The faster the
  particles move, the higher the frequency of the
  electromagnetic radiation.

49
22.3 Radiation

1. Radio waves send signals through the air.

50
22.3 Radiation

1. Radio waves send signals through the air.
2. You feel infrared waves as heat.

51
22.3 Radiation

1. Radio waves send signals through the air.
2. You feel infrared waves as heat.
3. A visible form of radiant energy is light waves.

52

• 11. What happens to the frequency of radiant
  energy as the temperature of the substance
  increases or decreases?

53

• The frequency of radiant energy increases as the
  temperature of the substance increases.

54
http//mail.jsd.k12.ca.us/bf/bflibrary/images/elec
tromagnetic-spectrum.jpg