Temperature:
The physical quantity that tells how warm or cold a body is with
respect to some standard body.
1.
2.
Proportional to the average kinetic energy of the particles of a
body.
Determines the direction in which thermal energy flows
between substances.
Thermal Energy
The total kinetic and potential energy of all the molecules of a
body due to their motion. (Internal Energy)
Heat
Thermal energy that is transferred from one object to another
because of the difference in temperature.
Temperature and Heat Measurements / Units
Temperature is measured by an instrument called a
Thermometer.
4 Types of Thermometers:
1.
2.
3.
4.
Solid
Liquid
Gas
Thermocouple
Solid Thermometers (Metal)
Contains a bi-metal coil (2 metals bonded together with different
expansion rates) which winds or unwinds when temperature
changes. (Typically brass and steel/iron)
The bimetallic strip thermometer, because it is made of metal, is
good at controlling very sensitive things. (House furnace, ovens,
refrigerator, etc.)
The longer the bimetal element the better accuracy.
Liquid Thermometer
Simply put, alcohol and mercury expand when heated. In a
standard bulb thermometer, this means the liquid will rise as the
temperature increases.

Mercury (silver): Used in hotter temps
 (-40ºC to boiling Point)

Alcohol (red or blue dye): Used in colder temps
 (-129ºC to 78ºC)
Glass tube filled with liquid (often mercury or alcohol) that
expands/contracts with air temperature
Gas Thermometer
A Gas filled bulb to which a pressure gauge is attached. Usually
this gas is hydrogen or helium. This is used on a large range of
temperatures.
Gas thermometers measure temperature by changes in the
pressure of a gas kept at constant volume
Thermocouple
A device consisting of two different conductors (usually metal
alloys) that produce a voltage, proportional to a temperature
difference, between either end of the two wires.
•
Applications include temperature measurement for large gas
ovens, diesel engines, and other industrial processes.
•
Temperatures range from -270ºC to 700ºC.
Note:
The three types of thermometers (solid, liquid and gas) all
operate on the principle that substances expand when
heated and contract when cooled.
Making of a thermometer:
http://www.youtube.com/watch?v=SZvAmvGQKEA
http://www.youtube.com/watch?v=XEv2Q7ASBPg
Four major Temperature scales:
(We will only deal with the 1st three)
•
•
•
•
Celsius
Fahrenheit
Kelvin
Rankine
Temperature is a physical quantity which gives us an idea of how
hot or cold an object is.
The temperature of an object depends on how fast the atoms and
molecules which make up the object can shake, or oscillate. As an
object is cooled, the oscillations of its atoms and molecules slow
down.
For example, as water cools, the slowing oscillations of the
molecules allow the water to freeze into ice. In all materials, a
point is eventually reached at which all oscillations are the
slowest they can possibly be.
The temperature which corresponds to this point is called
absolute zero. (Note that the oscillations never come to a
complete stop, even at absolute zero.)
Most people are familiar with either the Fahrenheit or the Celsius
scales, with temperatures measured in degrees Fahrenheit (ºF)
or degrees Celsius (ºC) respectively.
The Fahrenheit and Celsius scales coincide only at one
temperature: −40 degrees
(i.e. −40 °F and −40 °C describe the same temperature).
Fahrenheit scale:
 Water Freezes: 32º F
 Water Boils: 212º F
 Absolute zero: -459º F
Celsius scale:
 Water Freezes: 0º C
 Water Boils: 100º C
 Absolute zero: -273º C
The Kelvin (symbol: K) is a unit increment of temperature and is
one of the seven SI base units. The Kelvin scale is a
thermodynamic (absolute) temperature scale where absolute zero,
the theoretical absence of all thermal energy, is zero (0 K).
This definition also exactly relates the Kelvin scale to the Celsius
scale. Absolute zero—the temperature at which nothing could be
colder and no heat energy remains in a substance—is, by
definition, exactly 0 K and −273 °C.
Scientists - especially those who study what happens to things
when they become very, very cold - commonly use the Kelvin
scale, with temperatures measured in Kelvin (K).
This scale uses the same temperature steps as the Celsius scale,
but is shifted downward. On this scale, water freezes at 273 K
and boils at 373 K.
Kelvin scale:
 Water Freezes: 273 K
 Water Boils: 373 K
 Absolute zero: 0 K
FROM Celsius
Fahrenheit
Kelvin
9
TO Celsius
5
°F = (°C × ⁄5 )+ 32
°C = (°F − 32) × ⁄9
K = °C + 273
°C = K − 273
For temperature intervals rather than specific temperatures:
• 1 °C = 1 K
• 1 °C = 1.8 °F
FROM Fahrenheit
TO Fahrenheit
5
°F = (°C × ⁄5 ) + 32
5
°F = (K × ⁄5 )− 459
Celsius
°C = (°F − 32) × ⁄9
Kelvin
K = (°F + 459) × ⁄9
9
9
For temperature intervals rather than specific temperatures:
5
• 1 °F = ⁄9 °C
Celsius
Fahrenheit
FROM Kelvin
TO Kelvin
°C = K − 273
K = °C + 273
9
°F = (K× ⁄5 ) - 459
5
K = (°F +459)× ⁄9
Convert the following to the Celsius and Kelvin scale:
Celsius
Kelvin
68 ºF
20 ºC
293 K
5 ºF
-15 ºC
258 K
176 °F
80ºC
353 K
Convert the following to the Fahrenheit and Kelvin scale:
Fahrenheit
Kelvin
30ºC
86 ºF
303 K
5ºC
41 ºF
278 K
-20°C
-4 ºF
253 K
Ethyl alcohol boils at 78.5 °C and freezes at -117 °C. Convert
these temperatures to the (a) Fahrenheit scale and (b) Kelvin
scale.
Fahrenheit scale:
Boiling
173 °F
Freezing
-179 °F
Kelvin scale:
351.5 K
156 K
How do we measure heat?
calorie (cal)
• The calorie is the amount of heat needed to increase the temperature
of 1 gram of water by 1 °C.
British Thermal Unit (B.T.U)
• The amount of heat needed to raise the temperature of 1 lb. of water
1 °F.
Food Calories are measured in kcal
1 Cal = 1000 cal = 1kcal
Conversions:
•
•
•
1 cal. = 4.19 Joules
1 B.T.U. = 250 cal.
1 Calorie (food) = 1000 cal. = 1 kcal.
Mechanical Equivalent of Heat:
S.I.: 4.19 J of work converts to 1 calorie of heat.
B.E.: 778 ft-lbs of work converts to 1 B.T.U. of heat.
Formula for work:
W=J·Q
W = Work (Joules)
J = 4.19 J/cal (constant)
Q = Heat (calories)
a. How much work is required for a 1,500 Calories per day
person to be a couch-potato?
6,285,000 J
b. What is their Power consumption?
6,285,000 J / 86,400 seconds = 72.74 W
– We’re like light bulbs, constantly putting out heat