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Phys21: Temperature & Heat

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Stanley Eaton

on 16 February 2018

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Transcript of Phys21: Temperature & Heat

Temperature, Heat, and Expansion
Objectives
Define temperature in terms of kinetic energy
Describe common temperature scales
Define heat
Define thermal equilibrium
Distinguish between internal energy and heat
Describe how to measure heat
Compare specific heat capacities
Describe the effect of water's high specific heat on weather
Exemplify thermal expansion
Describe the behavior of water as its heated from freezing
Temperature, Heat, & Expansion Notes
o Define temperature in terms of kinetic energy.
Temperature
is how hot or cold something is. It measures the average kinetic energy of a substance: how much the parts of the substance move back and forth.
o
Describe the common temperature scales.
The
Celsius
scale
is the most common temperature scale. It sets 0 as the freezing point of water and 100 as its boiling point. It has replaced the
Fahrenheit scale
, which uses 32 for the freezing point of water and 212 for its boiling point, everywhere but in the US. The
Kelvin scale
is the SI temperature scale; it sets 0 as
absolute zero
, the temperature where all motion stops. To convert from C to K, add 273.
o
Define thermal equilibrium.
Thermal

equilibrium
is when two objects that are in thermal contact are the same temperature. Objects are in
thermal contact
when heat can flow between them.
o
Distinguish between internal energy and heat.
Internal energy
is the total of all the energies inside a substance.
Heat
is the energy that transfers from one substance to another because of a temperature difference. Think of heat as a verb, not a noun.
o
Describe how the quantity of heat that enters or leaves a substance is measured.
Heat can be measured using several units. The SI unit of heat is the
calorie
(cal). The calories on a food label are actually
kilocalories
, kcal, or 1000 cal, or Cal. The SI unit of heat is the Joule (J). 1 cal equals 4.184 J.
o
Compare the specific heat capacities of different substances.
The
specific heat capacity
of a substance measures its ability to store thermal energy. Iron has a low specific heat capacity while water has a high one because energy added to water makes it spin and stretch and vibrate as well as move back and forth.
o
Describe the effect of water’s high heat capacity on climate.
Since water has a high specific heat capacity, it takes a lot more energy from the
sun to warm up the ocean than the land. This means that islands don’t change temperature much, while inland locations do.
o
Exemplify the thermal expansion of solids.
Things generally get bigger when heated because thermal motion spreads out the molecules. Different things get bigger at different rates. In a
bimetallic strip
two different metals are welded together; they will curve when heated because of their different rates of thermal expansion.
Thermostats
use bimetallic strips to detect the temperature.
o
Describe the behavior of water as it is heated from 0 C to 15 C.
Water, like most substances, generally expands when heated. But between 0 C and 4 C, it shrinks. This is because cold water contains some ice crystals which are low density. As water goes from 0 C to 4 C, these crystals collapse and density increases.
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scales
heat and temperature
heat miser
specific heat
specific heat of water / global warming
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