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Heat. The Fire Down Below. Heat. A flow of energy from objects of higher thermal energy to objects of lower thermal energy Heat is measured in Joules (J) because it is a form of energy Described as a flow from hot to cold No such thing as “cold”. Temperature.

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slide1

Heat

The Fire Down Below

slide2
Heat
  • A flow of energy from objects of higher thermal energy to objects of lower thermal energy
  • Heat is measured in Joules (J) because it is a form of energy
  • Described as a flow from hot to cold
    • No such thing as “cold”
temperature
Temperature
  • Based on the motion of the particles in a substance
    • Fast motion = high temperature
    • Slower motion = lower temperature
  • Relatively describes how the particles collide with the surface of the thermometer
    • Collisions transfer energy
temperature scales
Temperature Scales
  • Fahrenheit
    • Common in the US
    • Freezing point of water is 32ºF
    • Boiling point of water is 212ºF
  • Celsius
    • Common in the rest of the world (SI)
    • Freezing point of water is 0ºC
    • Boiling point of water is 100ºC
temperature scales1
Temperature Scales
  • Kelvin
    • Used for science, as there are NO negative values
    • 0K is set at Absolute Zero, the temperature at which all particle motion stops
    • Freezing point of water is 273K
    • Boiling point of water is 373K
      • NOTE – 100K between freezing and boiling, so Kelvin uses the same degrees as Celsius
converting temperatures
Converting Temperatures
  • Fahrenheit to Celsius

Cº = 0.55 (Fº - 32º)

  • Celsius to Fahrenheit

Fº = (1.8 x Cº) + 32º

  • Celsius to Kelvin

K = C + 273

Adjusts for differences in Zero temperature

heat always flows
Heat always flows…
  • From low E to high E
  • From high E to low E
  • Across layers of density
  • Downwards, like gravity
the average motion of particles in a substance defines that substance s
The average motion of particles in a substance defines that substance’s…
  • Heat
  • Energy
  • Potential Energy
  • Temperature
the temperature scale used in the usa is
The temperature scale used in the USA is
  • Fahrenheit
  • Celsius
  • Kelvin
  • Thermocline
the temperature scale used in si is
The temperature scale used in SI is
  • Fahrenheit
  • Celsius
  • Kelvin
  • Thermocline
the temperature scale used in science is
The temperature scale used in science is
  • Fahrenheit
  • Celsius
  • Kelvin
  • Thermocline
thermal energy
Thermal Energy
  • Usually based on the total number of particles, as most temperatures in which we survive are relatively close together (-15ºF to 130ºF)
    • More particles = more thermal energy
      • Ex. boiling cabbage, frying foods, ocean water
thermal expansion
Thermal Expansion
  • As substances increase in temperature, the particles move apart
  • Substances expand and become less dense when heated
  • Substances shrink and become more dense when cooled
  • Explains expansion joints in bridges and concrete sidewalks
    • Water is one very important exception
examples of thermal expansion
Examples of Thermal Expansion
  • Notice the cracks that have formed in the concrete after some time of thermal expansion
conductors
Conductors
  • Allows heat (and electricity) to flow easily with little or no resistance
  • Heats up quickly, cools down quickly
    • Low “Specific Heat”
  • Usually metals
    • High density, free electrons
insulators
Insulators
  • Resist the flow of heat (and electricity)
    • High “Specific Heat”
  • Resisted heat can build up and cause the substance to burn
  • Usually nonmetals
    • Large molecules, no free electrons
heat transfer
Heat Transfer
  • Conduction
    • HTB direct particle contact
  • Convection
    • HTB mass movement of particles
  • Radiation
    • HTB invisible infrared radiation
what type of heat transfer describes why a dark shirt feels warmer on sunny days
What type of heat transfer describes why a dark shirt feels warmer on sunny days?
  • Conduction
  • Convection
  • Radiation
what type of heat transfer describes how a a c system changes room temperature
What type of heat transfer describes how a A/C system changes room temperature?
  • Conduction
  • Convection
  • Radiation
what type of heat transfer describes how lake water is hot on top and cold on bottom
What type of heat transfer describes how lake water is hot on top and cold on bottom?
  • Conduction
  • Convection
  • Radiation
specific heat
Specific Heat
  • Amount of energy that has to be lost or gained by a substance to change temperature
  • Note: Water has an incredibly high specific heat value due to the bonds between water molecules
specific heat1
Specific Heat

Q = m c T

where m is the mass of the substance

c is the specific heat value

T is the change in temperature of the substance (Tfinal – Tinitial)

homework 26
Homework 26
  • Pg. 163 – Questions # 1- 4
  • Pg. 170 – Questions # 1 - 4
layers and heat transfer
Layers and Heat Transfer
  • Layers trap air in a “dead air space”
  • More layers mean it’s harder to change temperatures between layers
    • Ex. double-paned windows, dressing in layers, layers of construction on a house
more on radiation
More on Radiation
  • Emitters are substances that give off radiation
    • Stars, campfires, space heaters, etc.
  • Absorbers capture radiation
    • Black shirts, asphalt, water
  • Reflectors return most of the radiation that is emitted towards them
    • Mirrors, aluminum foil, ice & snow
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