Internal energy: total amount of the energy of the particles that compose matter.
Thermal Energy Internal energy: total amount of the energy of the particles that compose matter.
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Thermal Energy Internal energy: total amount of the energy of the particles that compose matter
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Transcript of Thermal Energy Internal energy: total amount of the energy of the particles that compose matter.
Thermal Energy
Internal energy: total amount of the energy of
the particles that compose matter
What is the difference between heat, temperature and thermal
energy?• Heat: the quantity of thermal energy
transferred from a hotter to a colder object
• Temperature: the measure of the average kinetic energy of the vibrating particles that compose an object
• Thermal energy: the total amount of internal energy possessed by the particles that compose matter
When matter gets warmer, the atoms or molecules in the matter move faster.
All matter—solid, liquid, and gas—is composed of continually jiggling atoms or molecules, which have KE.
The higher the temperature of a substance, the faster the motion of its molecules.
This is also referred to as the Kinetic Theory—
a) all matter is made of atoms and molecules that are moving.
b) The higher the temperature, the faster the particles move.
c) Given the same temperature, heavier particles move slower than lighter particles.
21.1 Temperature
Measure temperature by showing expansion and contraction of a liquid in a glass tube. Three Scales (, Fahrenheit, Celsius and Kelvin)•Fahrenheit (32-212 F)•Celsius (0-100 C)•Kelvin is a universal scale with no upper limit. (0 K or absolute zero to …)
21.1 Temperature
This thermometer measures temperature on both Fahrenheit and Celsius scales.
21.1 Temperature
Puzzler
K = C + 273
Which is hotter, 500 K or 500 C?500 C, because 500 C is 773 K
273 K
21.1 Temperature
•Which has more thermal energy, a cup of boiling water or Lake Michigan in winter?
Lake Michigan! The water molecules are moving faster in the boiling cup of water, but there are vastly more water molecules in Lake Michigan.
Are the water molecules in an ice cube moving?
Yes. Motion of molecules stops at absolute zero.
What is the relationship between the temperature of a substance and the speed of its molecules?
21.1 Temperature
The higher the temperature of a substance, the faster is the motion of its molecules and the greater their average KE.
Physics and Particles
• Particle is a general term used to describe molecules, atoms and sub-atomic particles
Increasing Avg. KE
Increasing Temp.
solid
liquid
gas
Particle speed is increasing
Matter is changing state
melting
evaporation
condensation
freezing
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.
21.1 Temperature
highergreater
greater
Heat is the quantity of thermal energy transferred from a hotter to a colder substance.
1.Heat always flows from a substance with a higher temperature to a substance with a lower temperature.
2.Heat flows only when there is a difference in temperature.
3.Heat units are calories or joules.
21.2 Heat
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.
21.2 Heat hotter
colder
Entropy!
Flow from higher to lower energy state.
What causes heat to flow?
21.2 Heat
A difference in temperature between objects in thermal contact.
When a substance takes in or gives off heat, its internal energy changes.
21.4 Internal Energy
• Heat flows between two objects of different temperature until they have the same temperature. (2nd law of thermodynamics)
• The loss of thermal energy from the warmer object equals the gain of thermal energy for the cooler object
21.3 Thermal Equilibrium
What happens when a warmer substance comes in contact with a cooler substance?
Most forms of matter—solids, liquids, and gases—expand when they are heated and contract when they are cooled.
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.
21.8 Thermal Expansion
How 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.
• The liquid in the thermometer stops rising or falling when thermal equilibrium is reached (no more heat flow!)
Air temperature = Liquid temperature
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.
21.6 Specific Heat Capacity
21.6 Specific Heat Capacity
The specific heat capacity of a substance is the quantity of heat required to raise 1 g of a substance by 1 degree Celsius.
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).
21.6 Specific Heat Capacity
• 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
21.6 Specific Heat Capacity
highest
lowest
think!Which has a higher specific heat capacity—water or sand? Explain.
21.6 Specific Heat Capacity
think!Which has a higher specific heat capacity—water 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. Sand’s low heat capacity, shown by how quickly it warms in the morning and how quickly it cools at night, affects local climates.
21.6 Specific Heat Capacity
Good conductors have a low specific heat capacity!
A gram of water requires 1 calorie of energy to raise the temperature 1°C.
It takes only about one eighth as much energy to raise the temperature of a gram of iron by the same amount.
21.6 Specific Heat Capacity
The capacity of a substance to store heat depends on its chemical composition.
Winter Vs. Summer Heat Flow
• In winter
-Heat loss from inside (warmer) to outside (colder)
-Heating system must operate to transfer thermal energy from fuel to fluid to room to keep house warm
• In summer
-Heat gain from outside (warmer) to inside (cooler)
- Cooling system must operate to transfer incoming heat entering the house back to the outside
Why do we need heating systems?
• What do the green arrows represent?
• How does this heat flow affect the temperature of the air inside the home?
• Where does the energy come from that increases the temperature of the air inside the home?
Explain why the heat flow for a home is different in the winter vs. the summer.
Convection currents are produced by uneven heating.
a. During the day, the land is warmer than the air, and a sea breeze results.
22.2 Convection
Convection currents are produced by uneven heating.
a. During the day, the land is warmer than the air, and a sea breeze results.
b. At night, the land is cooler than the water, so the air flows in the other direction.
22.2 Convection
Generation of Sea BreezesDay
Land •low specific heat•heat and cools rapidly•less resistant to temperature change
Sea•high specific heat•heats and cools slowly•more resistant to temperature change
Sea breeze
Air above the land heats more rapidly and rises
Air above the sea remains cooler and moves on land to replace the land air that rose
Convection
Generation of Sea BreezesNight
Air above the water is warmer than the air above the land and rises
Air above the ground is cooler than the air above the water and moves over the sea to replace the sea air that rose
Land •low specific heat•heat and cools rapidly•less resistant to temperature change
Sea•high specific heat•heats and cools slowly•more resistant to temperature change
Land Breeze
Generation of Sea Breezes
The property of water to resist changes in temperature improves the climate in many places.
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.
21.7 The High Specific Heat Capacity of Water
Moderating Effect of Water
• 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.
Water’s capacity to store heat affects the global climate.
Water stores and hold heat well because of its high specific heat.
21.7 The High Specific Heat Capacity of Water
Gulf Stream brings warm water northeast from the Caribbean.
The Gulf Stream (warm water from equator)
meets
The Labrador Current (cold water from polar region)
Gulf Stream
Labrador Current
Thermal Front
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 sun’s energy per square kilometer.
21.7 The High Specific Heat Capacity of Water
http://www.sampleireland.com/weather-in-ireland-year-round.html
Cork
Edmonton
Same insolation angle, different climate due to proximity to water and the warming effect from the Gulf Stream
Continental Climate
Marine Climate
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.
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.
21.7 The High Specific Heat Capacity of Water
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.
Reason for the SeasonsReason for the Seasons
22
• The hemisphere tilted toward the Sun receives sunlight at higher angles than the hemisphere tilted away from the Sun.
• Higher insolation angle means greater intensity of radiant energy (the sun shines more directly on a smaller area).
Changing Angle of Sunlight
Summer in Northern Hemisphere
Season _________
Equinox or Solstice
Season _________
Equinox or Solstice
Season ________
Equinox or Solstice
Season _________
Equinox or Solstice
Identify the Seasons and the Equinox or Solstice, and comment about the number of daylight vs. night hours
_________
Season _________
Equinox or Solstice
Season _________
Equinox or Solstice
Season _________
Equinox or Solstice
Season _________
Equinox or Solstice
Identify the Seasons and the Equinox or Solstice
Equal day and night—12hr and 12 hr
Less night hours, more daylight hours
Less daylight hours, more night hours
spring
summer
fall
winter
Heat can be transferred by conduction, by convection, and by radiation.
http://www.nd.edu/~ysun/Yang/PhysicsAnimation/collection/transportP.swf
In conduction, collisions between particles transfer thermal energy, without any overall transfer of matter.
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.
22.1 Conduction
In convection, heat is transferred by movement of the hotter substance from one place to another.
22.2 Convection
Convection occurs in all fluids.
a. Convection currents transfer heat in air.
22.2 Convection
Hot, less dense fluid rises in the presence of cooler, more dense fluid.
Convection occurs in all fluids.
a. Convection currents transfer heat in air.
b. Convection currents transfer heat in liquid.
22.2 Convection
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.
In radiation, heat is transmitted in the form of radiant energy, or electromagnetic waves.
22.3 Radiation
Heat Transfer 1
• Which heat transfer occurs from particle to particle during direct contact of substances?
a) Conduction
b) Convection
c) Radiation
d)Conduction and Convection
e)Conduction, convection and radiation
Heat Transfer 1
• Which heat transfer occurs from particle to particle during direct contact of substances?
a) Conduction
b) Convection
c) Radiation
d)Conduction and Convection
e)Conduction, convection and radiation
Heat Transfer 2
• Which heat transfer can occur through a vacuum or through matter?
a) Conduction
b) Convection
c) Radiation
d)Conduction and Convection
e)Conduction, convection and radiation
Heat Transfer 2
• Which heat transfer can occur through a vacuum or through matter?
a) Conduction
b) Convection
c) Radiation
d)Conduction and Convection
e)Conduction, convection and radiation
Heat Transfer 3
• Which heat transfer is based on density differences in a substance and gravity?
a) Conduction
b) Convection
c) Radiation
d)Conduction and Convection
e)Conduction, convection and radiation
Heat Transfer 3
• Which heat transfer is based on density differences in a substance and gravity?
a) Conduction
b) Convection
c) Radiation
d)Conduction and Convection
e)Conduction, convection and radiation
Heat Transfer 4
• Which heat transfer occurs through the movement of the heated substance?
a) Conduction
b) Convection
c) Radiation
d)Conduction and Convection
e)Conduction, convection and radiation
Heat Transfer 4
• Which heat transfer occurs through the movement of the heated substance?
a) Conduction
b) Convection
c) Radiation
d)Conduction and Convection
e)Conduction, convection and radiation
Heat Transfer 5
• Which heat transfer is characterized by transmission by electromagnetic waves?
a) Conduction
b) Convection
c) Radiation
d)Conduction and Convection
e)Conduction, convection and radiation
Heat Transfer 5
• Which heat transfer is characterized by transmission by electromagnetic waves?
a) Conduction
b) Convection
c) Radiation
d)Conduction and Convection
e)Conduction, convection and radiation
Heat Transfer 6
• Which heat transfer processes can only occur through matter?
a) Conduction
b) Convection
c) Radiation
d)Conduction and Convection
e)Conduction, convection and radiation
Heat Transfer 6
• Which heat transfer processes can only occur through matter?
a) Conduction
b) Convection
c) Radiation
d)Conduction and Convection
e)Conduction, convection and radiation
Most of the heat from a fireplace goes up the chimney by convection. The heat that warms us comes to us by radiation.
22.3 Radiation
• Radiation is caused by moving electrons or charged particles in matter. The faster the particles move, the higher the frequency of the electromagnetic radiation.
a. Radio waves send signals through the air.
22.3 Radiation
a. Radio waves send signals through the air.
b. You feel infrared waves as heat.
22.3 Radiation
a. Radio waves send signals through the air.
b. You feel infrared waves as heat.
c. A visible form of radiant energy is light waves.
22.3 Radiation
11. What happens to the frequency of radiant energy as the temperature of the substance increases or decreases?
• The frequency of radiant energy increases as the temperature of the substance increases.
http://mail.jsd.k12.ca.us/bf/bflibrary/images/electromagnetic-spectrum.jpg
