Transcript Dr. York`s Physical Science Notes on Heat, Temperature

Chapter 14
Heat and Temperature:
Temperature
Energy Transfer
Using Heat
TN Standards
• CLE 3202.2.3 – Examine the applications
and effects of heat energy
• CLE.3202.2.6 – Investigate the Law of
Conservation of Energy
• CLE.3202.TE.3 – Explain the relationship
between the properties of a material and
the use of the material in the application of
a technology
TN Standards
• SPI.3231.2.1 – Relate temperature
changes with the changes of kinetic
energy and the flow of heat energy
Bellwork
• What is temperature?
• Average kinetic energy of particles in a
material
Section 1 - Temperature
• Key Questions:
• 1] What does temperature have to do with
energy?
• 2] What three temperature scales are
commonly used?
• 3] What makes things feel hot or cold?
Temperature and Energy
• Kinetic theory of matter
– Matter is made of small particles always moving
– Higher temperature, more motion
– Large particles move slower
• The temperature of a substance is
proportional to the average kinetic energy of
the substance’s particles
• All particles have kinetic energy ( atomic )
Measuring Temperature
• As materials are heated, they expand
• Thermometers rely on expansion of liquids
– Mercury or Alcohol
• Thermostats rely on expansion of metals
Temperature Scales
• Units: Fahrenheit ( English )
and Celsius ( metric )
• Fahrenheit is English
• Celsius/Kelvin is metric
• Kelvin is an absolute scale
– Absolute zero at -273.15 oC
Temperature Scales - Converting
• Celsius  Fahrenheit:
TF = 1.8*TC + 32.0
• Fahrenheit  Celsius:
TC = ( TF – 32.0 ) / 1.8
Temperature Scales - Converting
• Celsius  Kelvin:
TK = TC + 273.15
• Kelvin  Celsius:
TC = TK - 273.15
Temperature & Energy
Transfer
• When you feel “hot” or “cold” you are
detecting a temperature difference
• You are also feeling the affects of energy
transfer
• Temperature changes indicate an energy
transfer – temperature difference between two
objects is felt as heat
• Heat is the energy transferred between
objects of different temperature
Section 2 – Heat Transfer
• Key Questions:
• 1] How does energy transfer happen?
• 2] What do conductors and insulators do?
• 3] What makes something a good conductor
of heat?
Energy Transfer ( Heat Flow )
• What is happening in each picture
• Explain how heat is flowing ( ID how heat
goes from one object to another )
• What might be happening on the
atomic level?
Different Methods of Transfer
Different Methods of Transfer
• Conduction occurs between objects in direct
contact
• Thermal Conduction–heat source is one object
Different Methods of Transfer
• Convection results from the movement of
warm fluids ( in contact with heat source )
• Warm fluids rise
– Cool when away from heat
• Cool fluids fall
• Convection current –
Path of warm/cool fluids
Different Methods of Transfer
• Radiation does not require physical
contact between objects
• Energy transferred as
electromagnetic waves
Conductors & Insulators
• A conductor is a material
through which energy can be
easily transferred as heat
• An insulator is a material that
transfers energy poorly
• Heat energy is transferred
through particle collisions
Conductors & Insulators
• Heat energy is transferred through
particle collisions
• Gases – poor conductors
– Why?
• Denser materials usually are
better conductors than less dense
• Metals – very good conductors
• Plastics – poor conductors
Bellwork – 11/21/14
• When you melt ice, is heat going to be
added to the water, or removed from it?
• Add heat
Specific Heat
• Determines how easily energy
can be transferred as heat
• How much energy is needed
to change the temperature of a
substance by a certain amount
Specific Heat
• Amount of energy needed to raise the
temperature of 1 kg of substance by 1 K
• 1 degree change in C = 1 degree change K
• Energy = specific heat x mass x temp change
• Energy = cmΔT
• c = energy /(mΔT)
Specific Heat
• Temperature does not change when phases do;
energy goes into phase change - not
temperature adjustment
• Latent heat ( melting ) & Heat of Fusion ( evap )
– Gives amount of energy needed for phase change
Heat Flow Conceptual Practice
• Scenarios – Explain what is happening:
• 1] You pick up a coffee cup and it is hot
• 2] You touch a glass of cold SCHAWEET tea
• 3] A breeze makes you shiver
Heat Flow Conceptual Practice
• Which substance can you heat the quickest?
• One with a large or small heat capacity?
Heat Flow Math Practice
• How much energy must be transferred as
heat to 200 kg of water ( c = 4,186 J/kg/K ) in
a bathtub to raise its temperature from 25 oC
to 37 oC?:
Specific Heat Example
• The temperature of a substance increases by
7 K when 1850 J is added to a 5 kg quantity of
the substance. What is the specific heat ( c )?
Specific Heat Example
• The temperature of a substance increases by
7 K when 1850 J is added to a 5 kg quantity
of the substance. What is the specific heat ( c
)?
• 1850 / (5 * 7 ) = 52.9 J/(kg*K)
Specific Heat Example
• Temperature of 2.5 kg ethanol is 47 oC. What
will the final temp be if 90,000 J of heat
energy [ c = 2440 J/(kg*K) ].
Specific Heat Example
• Temperature of 2.5 kg ethanol is 47 oC. What
will the final temp be if 90,000 J of heat
energy [ c = 2440 J/(kg*K) ].
• ∆T = 90000/(2.5 * 2440) = 14.75 degrees C
or K
• Final Temp = 14.75 + 47 = 61.8 oC
Section 3 – Using Heat
• Key Questions:
• 1] What happens to heat energy when it is
transferred?
• 2] What do heat engines do?
Thermodynamics
• 1st Law – total energy
used in any process is
conserved, whether that
energy is transferred as
work, heat, or both.
Thermodynamics
• 2nd Law – energy
transferred as heat
ALWAYS moves from
higher to lower
temperature. Another
way of saying “Energy is
always conserved.”
Thermodynamics
• Entropy – randomness
or disorder of a system
• Thermo [3rd Law] tells
us that total entropy of
the universe is ALWAYS
increasing ( natural
tendency )
What is a System?
• A “system” is defined as the area, volume
and/or group of objects being analyzed
• Systems can be open or closed
• Closed system – like a can of coke or soup
that has not been opened
• Open system – once you open that can of
coke or soup
Heat Engines
• Heat Engines – chemical energy is
converted into mechanical energy by
combustion
Heat Engines
Using Heat
• Rubbing alcohol applied to the skin – what
happens/what do you observe?
• Why?
Using Heat
• Rubbing alcohol applied to the skin – what
happens/what do you observe?
• Why?
Using Heat
• cooling/heating processes utilize this
• SWEATING!
• Fluids—liquids & gases—are chosen that
easily evaporate and condense
• Evaporation – energy is absorbed by the
fluid/sweat ( from surrounding air )
• Condensation – energy is released by the
fluid/moisture ( absorbed by air )