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What is
a Measurement System? |
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A measurement system is part of our language; it allows us to communicate
better. For example, if you have a nice meal and ask for the recipe, it is
convenient that someone can say to put in so many ounces of this ingredient and
so many cups of that. As another example, if you need some wood to build
something, one can go to a shop and say that you need a given number of feet of
wood. This is only possible because we have a set of names (e.g. foot, pound,
gallon), each of which mean a given amount of something. In simple terms, this
is what a measurement system is:
- An agreed set of names. In formal terms, these are known as measurement
'units'.
- Where each name (unit) defines a specific amount of something
The most common types of measurement are:
- Length (e.g. inches, feet). This can also be called width, height or
distance, but it is still the same set of measurement units.
- Weight (e.g. ounces, pounds)
- Volume (e.g. quarts, gallons)
- Time (e.g. seconds, hours)
- Temperature (e.g. degrees Fahrenheit)
Most other measurements are a combination of the above. For example, speed is
a measure based on length and time. When we say a car is going 60 miles per
hour, this means it is going a length (distance) of 60 miles in a
time of one
hour.
In addition, there are a few other types of measurement, but they are not
used day-to-day by most people. These include strength of electrical current (SI
measurement unit 'ampere'), brightness (SI measurement unit 'candela') and
amount of substance at the atomic level (SI measurement unit 'mole').
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How Many
Different Measures are there? |
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In most measurement systems, there are the five common measurements listed
above (length, weight, volume, time and temperature). Each of these consist of a
number of different 'units'. For example, length can be measures in units of
inches, feet, yards, miles, and so on. Weight can be measured in ounces, pounds,
tons, etc.
In addition to the measurement units that most people immediately recognise,
there are hundreds of measurement units which are less well known. The height of
horses is commonly measured in 'hands', where a hand is the width of a person's
palm, which is defined as 4 inches. So, if someone says that a horse is 16 hands
high, it is 64 inches high.
Another example is the 'barrel', which is mainly used in the agricultural,
petroleum and alcohol industries. However, different industries uses
different sizes of barrel, leading to 7 different barrel units in the USA
system. These are US cranberry (95.5 liters), US dry (115.628 liters), US liquid
(119.24 liters), US federal (117.348 liters), US federal proof spirits (151.416
liters), US drum (208.4 liters), US petroleum (135 kg.), US petroleum
statistical (158.99 liters).
In total, the USA system of measurement has several hundred different
measuring units. However, the average person would only use 20 or 30 of these on
a regular basis, such as length units (inches, feet, yards, miles), weight units
(ounces, pounds, tons), volume units (teaspoon, tablespoon, fluid ounce, cup,
pint, quart, gallon), time units (seconds, minutes, hours, days, weeks, years,
decades, centuries) and temperature
(degrees Fahrenheit).
The Imperial system (originating in England) of measurement has a similar
number of measuring units. Many of the units in the Imperial system are the same
as the USA system, but not all.
Other societies (e.g. the Romans, Greeks, ancient Egyptians) also had their
own measurement systems and measuring units. However, these are no longer used.
The only measurement systems still in use are:
- Imperial Measurement System. This system developed in the United
Kingdom (UK) and was used in both the UK and its colonies. The UK and its
ex-colonies have now mainly switched to the metric system.
- USA Measurement System. Prior to declaring independence, the
United States used the Imperial measurement system. After independence, it
changed some of the existing measures and developed a number of new
measures. The USA measurement system is now used only in the USA and two other
countries (Liberia and Burma). Although there are many units that exist in both the USA and
Imperial measurement systems, some of the units have the same size (e.g.
inch, foot, yard) whereas some are slightly larger or smaller in one system
than the other (e.g. gallon, ton).
- SI System. The metric system was developed in France during the
early 1790s. In 1795 it became the official measurement system of France. In
1960 the metric system was officially renamed to "Système
International d'Unités" (International System of Units), and given the
official symbol SI. Almost all countries have now adopted the SI, with the
USA being the notable exception.
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How Many
Different SI Measures are there? |
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In the USA measurement system and the Imperial Measurement System there are a
large number of different measures, due largely to the fact that different sizes
can have different unit names. For example, length can be measured in inches,
feet, yards or miles. In the metric system there is only one unit name for
length, which is the meter. To describe bigger or smaller units, one puts a
prefix in front of the name. For example, a kilometer is 1000 meters ('kilo'
means 1000). A centimeter is a hundredth of a meter ('centi' meaning1/100th).
So whereas the USA system has a number of different units for length, the metric
system has only one measure (the meter).
In fact, the metric system has only seven fundamental units of measurement.
All other measurements are based on a prefix in front to indicate larger or
smaller amounts, or a combination of the measures. Of the seven units of
measurement, the ones used on a daily basis are:
- Meter. This is a measure of length. It is equal to approximately
39 inches (just over a yard). Note that some countries use the alternative
spelling of 'metre' instead of 'meter'.
- Kilogram. This is used as a measure of weight (although
technically it is a measure of 'mass'). A kilogram is equal to approximately
2.2 pounds.
- Celsius. This is a measure of temperature. 0 degrees Celsius is
equal to 32 degrees Fahrenheit (the point at which water freezes) and 100
degrees Celsius is equal to 212 degrees Fahrenheit (the point at which water
boils). Officially, the SI has replaced Celsius as the measure of
temperature by another measure 'Kelvin'. However, almost everyone continues
to use the older measure of Celsius and undoubtedly will continue to do so
for quite some time, so this web site fill follow the common convention of
using Celsius as the SI measure of temperature.
- Second. This is the measure of time.
There are a number of other measures based on these 'base' units. For
example, one might say that a car is going 60 kilometers an hour. This is 60 *
1000 (note: 'kilo' is one thousand) meters in an hour (3600 seconds).
One of the most common units based on the above is the 'litre'. A litre is
the amount corresponding to a cube which is 1/10th of a meter in
size. It is approximately equal to a quart.
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