Temperature and HeatTemperature and Heat Temperature and Thermometers

Is it hot or cold?

Mercury vs. alcohol• Expansion or contraction of a material

Electrical resistance and infrared radiation

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Temperature and HeatTemperature and Heat Temperature scales

Reference points for setting the scale

• Why use water?

Triple point of water

• Solid, liquid and vapor all exist at the same time04/21/2304/21/23 APHY101APHY101 22

Temperature and HeatTemperature and Heat Absolute zero

Lowest temperature theoretically possible

• Lowest achieved is ~ 1x10-9 K• Average in space ~ 3 K

The KE is removed but not the quantum energy inside the atom – the electrons don’t stop moving

Is there a maximum temperature?04/21/2304/21/23 APHY101APHY101 33

Temperature and HeatTemperature and Heat Heat

Transfer of thermal energy between objects of different temperatures.

• Symbol: Q Unit: joules ( J )

High temperature does not always mean high thermal energy

Other units: BTU, calorie, Calorie (food)

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Temperature and HeatTemperature and Heat Internal energy

Sum of KE (linear, rotational, vibrational) and PE (chemical bonds within and between molecules)

• Model

The thermal energy of the system

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Temperature and HeatTemperature and Heat Thermal expansion

Most substances expand as their temperature increases and contract when cooled

Each material has a different expansion rate

Examples: Pyrex glass, dental fillings, bridges, concrete

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Temperature and HeatTemperature and Heat Thermal expansion of water

Water expands as it cools from 4°C to 0°C

• Effect on ponds, lakes and roads during winter

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Temperature and HeatTemperature and Heat Specific heat

A constant that relates heat per unit mass and temperature change in a material

• Metals have low values and water has a high value

Thermal inertia• Climate: land vs. oceans• Pizza: crust vs. sauce

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Temperature and HeatTemperature and Heat Conduction

Energy transfer due to particle contact• Atoms, molecules and electrons (metals)

Insulators and conductors• Building materials• Layers of clothing

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Temperature and HeatTemperature and Heat Convection

Energy transfer due to the motion of a fluid

• Currents are formed

Hot fluids rise and cold fluids sink• Cooling occurs when a fluid expands• Weather and climate

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Temperature and HeatTemperature and Heat Radiation

Energy carried by electromagnetic waves

• They can travel through empty space (vacuum)

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Temperature and HeatTemperature and Heat Radiation

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UVIRRadio

Temperature and HeatTemperature and Heat Radiation

All objects are emitters and absorbers of radiation

The rate of emission/absorption depends on the difference in T of the objects

Global warming• The greenhouse effect

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