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The temperature of an object is the
average energy of its molecules. On the other hand, Heat
is the total energy of the object. The faster a molecule
moves, the more energy it has. Temperature is related to
the average speed of the molecules. It is a measurement
of the intensity of the heat.
Since you are an observant and curious
person, you may have the following questions that you
want answered:
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How is temperature measured?
-
What is the coldest possible
temperature?
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How do you convert from Fahrenheit
to Celsius?
How temperature is measured
Temperature is measured by noting how
much a material expands from its size at a given
starting point--such as the freezing point of water. A
unit of measurement (1 degree) is defined, and all
temperatures are then multiples of that unit.
You have probably noticed that most
materials expand when heated. The higher the
temperature, the more things expand. That principle can
be used to measure the temperature. Many thermometers
use the expansion of liquids in a tube to measure the
temperature.
Around 1700, a German scientist Gabriel
Fahrenheit invented the thermometer by putting water in
a glass tube. The warmer the temperature, the higher the
water went up the tube.
Now, to be able to measure temperature
with numbers, Fahrenheit had to determine a unit of
measurement. Just as the measurement of weight and
length was based on multiples of an arbitrary unit of
measurement (the pound, gram, inch, meter), the
measurement of temperature is based on an arbitrary unit
of measurement�the degree.
Fahrenheit used his body temperature as
100 degrees and the freezing temperature of saturated
salt water as 0 degrees. He marked those levels on his
thermometer and divided the scale into 100 parts for
each degree.
The choice of 100 degrees and 0 degrees
were unfortunate. Fahrenheit's metabolism was higher
than most people, so 100 degrees for him resulted in
98.6 degrees F as the body temperature for the average
person.
Although ocean water freezes at 28
degrees F, water saturated with salt--such that it
collects on the bottom--freezes at a much colder
temperature. Fahrenheit designated that temperature as
zero. But that certainly is not the coldest temperature
you can experience in winter weather. It also makes the
freezing point of water an awkward 32 degrees F.
What is more amazing than this poor
selection of temperature units is the fact that
countries such as Great Britain and the United States
embraced that system of measurement. England has since
gone to the the Celsius scale.
About 20 years after Fahrenheit invented
the thermometer, Swedish professor Anders Celsius
defined a better scale for measuring temperature. He
proposed using the boiling point of water as 100 degrees
and the freezing point of water as 0 degrees. This made
a lot more sense and was called the centigrade system. (Centi-
means hundred and centigrade means divided into 100
units.)
The centigrade scale was used until the
1960s, when the scientific community renamed it the
Celsius system in honor of the inventor. Some people
still call it the centigrade scale.
Europe and most of the world measures
temperature in Celsius units, but for some reason the
United States adopted the cumbersome Fahrenheit system
of measuring temperature.
Since temperatures often go below the
freezing point of water in the winter, that liquid has
been replaced for use in a thermometer. At one time
silver-colored Mercury was used. It is the most
accurate, but since it is dangerous to the environment
it is only used today by physicians.
The red liquid in many thermometers is
colored alcohol, which does not freeze until around -90
degrees F.
Another popular device is the bimetal
thermometer that is used in many home thermostats. It
consists of a copper and a steel strip of metal attached
to each other. Since copper expands faster than steel,
it causes the strip to bend. When it bends, it can make
an electrical contact to start up your furnace.
Usually, these bimetal strips are in a
coil. If you have an opportunity, take off the cover of
your thermostat and observe the curved metal strip.
The newest type of thermometers are
electronic. They often use electrical resistance to
measure temperature and show the degrees in digital
numbers.
The coldest possible temperature
As the temperature goes down, the
average energy and speed of the molecules decreases.
There is a temperature at which the molecules stop
moving. That temperature is called Absolute Zero. This
coldest possible temperature is -273 degrees C or -460
degrees F.
For scientific work with the energy of
molecules, it is good to have a starting point where
nothing is moving. Thus a scale was determined, based on
the Celsius scale, but with a starting point at absolute
zero. This is called the Kelvin scale.
Absolute zero based on Fahrenheit is
called the Rankine scale. Since most scientific work is
done based on the Celsius scale, the Rankine scale for
absolute temperatures is seldom used.
Some strange things happen near absolute
zero. One thing is that electricity moves through a wire
without resistance. Another is that the gas Helium
becomes a liquid that flows up and over the sides of a
glass container.
The formula to convert Celsius to
Fahrenheit is:
F = 9*C/5 + 32
In other words, if C = 100 degrees
(boiling point of water), then
F = (9 x 100) / 5 + 32 = 212 degrees F
The formula to convert Fahrenheit to
Celsius is:
C = 5*(F - 32)/9
In other words, if F = 50, then
C = 5*(50 - 32)/9 = 5*(18)/9 = 10
degrees C
Converting from degrees Celsius to
Kelvin is simple.
K = C + 273
Thus, if C = 10 degrees, the Kelvin
temperature would be 283 degrees K.
The temperature of an object is the
average energy of its molecules. The fact that materials
expand when heated resulted in the invention of the
thermometer. There are three commonly used systems for
measuring temperature: Fahrenheit, Celsius, and Kelvin. |
