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Temperature, Heat and Expansion

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100 F is cow body temp (rectal) Water freezes at 32 F boils at 212 F ... Proportional to temperature change and original length of material ... – PowerPoint PPT presentation

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Title: Temperature, Heat and Expansion


1
Temperature, Heat and Expansion
  • Physics 1010
  • Dr. Don Franceschetti
  • March 28, 2005

2
Temperature
  • Of an object is a measure of the average random
    kinetic energy of atoms or molecules that make up
    that object
  • Almost all substances expand when the temperature
    is raised
  • Three temperature scales in use

3
Celsius (centigrade) Temperature
  • Water freezes at 0 C
  • Water boils at 100 C
  • Problem negative numbers are hard to avoid

4
Fahrenheit Temperature
  • G. D. Fahrenheit 1686-1736
  • Pick your story
  • 0 F is temperature of ice/salt bath
  • 0 F is coldest winter temperature
  • 100 F is hottest summer temp
  • 100 F is human body temp
  • 100 F is cow body temp (rectal)
  • Water freezes at 32 F boils at 212 F
  • 180 degrees between freezing and boiling
  • T( C)(T( F)-32)5/9

5
Kelvin (Absolute) Temperature
  • All gases in limit of high temp and low density
    loose 1/273 rd of their volume for each one C
    decrease in temperature
  • If substances remained as ideal gases, there
    would be no volume left at -273 C
  • T(K) T(C) 273.15, absolute zero is coldest
    possible temperature.
  • Even though gases all condense when cold enough,
    this is still true.

6
More precisely
  • Temperature is a measure of the average motional
    kinetic energy of molecules in the material.
  • Microwave increases rotational kinetic energy of
    water molecules, these bump into others.
  • A thermometer measures its own temperature!

7
Heat
  • Heat is energy in transit from one body to
    another
  • Internal energy is the grand total of all
    energies inside a substance
  • Is measured in joules or calories (people used to
    think of heat as a fluid--caloric)
  • I calorie is heat required to raise temperature
    of one gram of water by 1 degree Celsius
  • 1 calorie is 4.184 joules
  • Food Calorie 1000 calories, is energy released
    on total combustion of food

8
Count Rumford
  • Born in 1753 in Woburn MA but went to Britain in
    1776
  • Disproved caloric theory by drilling cannons
  • Invented many things for the kitchen

9
Specific Heat (thermal inertia)
  • The specific heat capacity of any substance is
    the quantity of heat required to change the
    temperature of a unit mass of the substance by 1
    degree
  • Water has a high capacity, important effects on
    climate

10
Thermal Expansion
  • Proportional to temperature change and original
    length of material
  • Bimetallic strips will curve when temperature
    changes, basis of thermostat.
  • Gaps in roads and sidewalks must be provided
  • Most materials expand at a nearly constant rate
    with temperature. Water does not

11
Water thermal expansion
12
Homework 4, due April 4, 2005
  • RQ15.1 Why does a penny become warmer when it is
    struck by a hammer?
  • RQ15.8 On which temperature scale does the
    average kinetic energy of molecules double when
    the temperature doubles.
  • E15.15 Why would a watermelon stay cooler for a
    longer time than sandwiches when both are removed
    from a cooler on a hot day?

13
Homework 4, contd
  • E15.21 Desert sand is very hot in the dat and
    very cool at night. What does this tell you
    about its specific heat.
  • E15.38 Why are incandescent bulbs typically made
    of very thin glass?
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