Heat and Thermal Energy

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Heat and Thermal Energy

• Molecules in the mosh pit

10/10/2013
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Todays Warmup

• Today, something a little different.
• Here are some totally cool sidewalk chalk
  drawings (anamorphic illusions) by British artist
  Julian Beever.

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Todays Warmup
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Todays Warmup
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Todays Warmup
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Todays Warmup
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Todays Warmup
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Todays Warmup
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Todays Warmup
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Todays Warmup
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Todays Warmup
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Todays Warmup

• Radiation, Conduction, Convection
• Hip-hop Science

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Todays Objectives

• Intro to heat and thermal energy
• heat vs temperature
• Measurement of heat
• Definition of specific heat
• Thermal energy BrainPop
• CPS quiz next class period!
• energy and heat

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Thermal Energy
Notes
Questions Vocabulary words Formulas Main
Ideas Possible Test Questions Key Words
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Summary of the notes and information learned
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What is temperature

• Temperature is a measurement used to quantify the
  sensations of hot or cold, but what does
  temperature actually measure?
• Molecules are constantly moving- they have
  kinetic energy. Some are moving quickly, some
  slowly, up, down, sideways They bounce off each
  other like dancers in the mosh pit.
• What happens when you heat molecules?

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What is temperature

• Heated molecules have more energy. They speed up
  and bounce around more. If we heat a cup of water
  all of the molecules increase their speed and
  random motion.
• The temperature of an object measures the average
  kinetic energy of its molecules.

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Thermal Energy (aka Heat)

• The thermal energy of an object or substance is
  the TOTAL (SUM) energy (potential and kinetic) of
  its molecules
• Mass, properties of the substance and temperature
  are involved here
• For example- one cup of boiling water has less
  thermal energy (heat) than one gallon of boiling
  water- even though both are at the same
  temperature 100 degrees C (212 degrees F).

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Kinetic Theory

• Kinetic Theory helps explain heat energy and heat
  transfer.
• It says all matter is made of constantly moving
  particles.
• Lets see that in action!

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Kinetic Theory

• Lab Activity
• Work in groups of 4 One paper/graph per two
  students
• Materials
• Stopwatch
• 250 ml glass beaker
• 100 ml ice
• Thermometer
• Hot plate
• Take temperature measurements every 30 seconds
  until Mr. Rasure says to stop
• Graph results

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Kinetic Theory
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Temperature Scales

• The English system uses Fahrenheit to measure
  temperature.
• In this scale water freezes at 32 degrees and
  water boils at 212 degrees.
• Room temp is about 68 degrees.

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Temperature Scales

• Most of the world (and all scientists) use the
  Celsius scale- measured in degrees centigrade
• Water freezes at 0 degrees Celsius and boils at
  100 degrees.
• Room temperature would be about 25 degrees.

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Temperature Scales

• To convert between the two use these formulas
• F 1.8C 32
• C (F 32) / 1.8

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Temperature Scales

• The Kelvin scale and absolute zero
• This temperature scale is named after the British
  mathematician and physicist William Thomson
  Kelvin, who proposed it in 1848.
• Absolute zero is the lowest possible temperature
  where nothing could be colder, and no heat energy
  remains in a substance. Absolute zero is the
  point at which molecules do not move!

Kelvin Celsius Fahrenheit
Water boils 373.16K 100C 212F
Water freezes 273.16K 0C 32F
Absolute zero 0K -273.16C -459.7F
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Conversion Practice

• 1. Body Temperature 98.6 F (Convert to C)
• 1. C (F - 32) X 5/9 C (98.6 - 32) X 5/9
  66.6 X 5/9 37C
• 2. Boiling Temp of Water 212 F (Convert to C)
• 2. C (F - 32) X 5/9 C (212 - 32) X 5/9
  180 X 5/9 100 C
• 3. Moderate Oven 175 C (Convert to F)
• 3. F (C X 9/5) 32 F (175 X 9/5) 32
  315 32 347 F
• 4. Hot Summer Day 38 C (Convert to F)
• 4. F (C X 9/5) 32 F (38 X 9/5) 32
  68.4 32 100.4 F

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How does a thermometer work?

• Thermometers work through thermal expansion.
• As molecules are heated the gain kinetic energy
  and the volume of a substance increases
• The liquid in a thermometer (colored alcohol or
  mercury) expands and rises in the glass tube as
  it gets warmer.
• Digital thermometers work because of electrical
  resistance. The warmer a wire the more resistance
  it has to the flow of electrons.

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Specific Heat

• Different substances require different amounts of
  heat to rise to the same temperature- a wood
  handled pot of boiling water is much cooler to
  the touch than a steel handled pot of boiling
  water.
• Why?
• Conductors and Insulators

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Specific Heat

• Specific heat is a property of a substance that
  tells how much the temperature goes up when a
  given amount of heat is applied.
• Specific Heat amount of energy needed to raise
  the temperature of 1 g of material 1 C
• A large/high specific heat means you have to put
  in a lot of energy for each degree increase in
  temperature.

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Specific Heat

• Water has a high specific heat
• Water can absorb more heat/energy before its
  temperature rises

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Specific Heat Formulaas shown on TAKS chart
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8368 J/g C
Lets Practice for candy!
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Specific Heat
Ex Calculate the amount of heat required to
raise the temperature of 78.2g of water from 10?C
to 35?C. Specific heat of water 4.18
J/(g?C) Heat 4.18 J/(g?C) (78.2g)(35?C -
10?C) 8171.9 J
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Specific Heat
Ex Calculate the amount of heat required to
raise the temperature of 78.2g of water from 10?C
to 35?C. Specific heat of water 4.18
J/(g?C) Heat 4.18 J/(g?C) (78.2g)(35?C -
10?C) 8171.9 J
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Thermodynamics- how heat moves

• Thermal energy always travels from higher
  temperatures to lower temperatures
• Thermal energy (heat) can be transferred in three
  ways
• Conduction
• Convection
• Radiation

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Thermodynamics- how heat moves

• Conduction- the transfer of heat by the direct
  contact of particles of matter

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Thermodynamics- how heat moves

• Heat continues to transfer until both objects
  reach thermal equilibrium (same temperature)
• Materials that transfer heateasily are called
  conductors.Those that transfer thermalenergy
  poorly are calledinsulators.

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Thermodynamics- how heat moves

• Why would a Styrofoam cup not transfer the heat
  of hot coffee to your hand as quickly as a metal
  cup???

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Thermodynamics- how heat moves

• Convection- the transfer of heat by the actual
  motion of a fluid (liquid or gas) in the form of
  currents.

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Thermodynamics- how heat moves

• Radiation- the transfer of heat by
  electromagnetic waves.
• Does not require matter to travel through (and
  thus can travel through the vacuum of space)
• Transfers heat in all directions
• Requires no contact
• Can go through transparent materials

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Thermodynamics- how heat moves

• Electromagnetic waves can be
• Infrared
• Visible light
• Ultraviolet
• The heat we enjoy from the sun comes to us as
  electromagnetic waves (radiation)

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Thermal Energy
Notes
Questions Vocabulary words Formulas Main
Ideas Possible Test Questions Key Words
Notes
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Summary of the notes and information learned
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Todays Assignment

• There are many types of heating and cooling
  systems found in the world around us including
  weather systems, living systems, and mechanical
  systems. Chapter 29 (pg. 471) gives us an
  overview of these systems.
• Lets use this chapter to answer the questions
  shown on page 489 (Concept Review 1 through 10).
  Write both the question and a complete answer.
  Use a clean sheet of paper you can turn in when
  complete.

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CPS Quiz and Homework Sheet

• You may use your notes/lab-book, BUT you may not
  share with your neighbor!
• Subjects covered include
• Energy
• Heat
• Thermodynamics

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Test Formulas
F 1.8C 32 C (F 32) / 1.8
Ohms Law I V/R (Iamps, Vvolts, Rohms of
resistance)
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Make it a great day Mustangs!