The Metric System Simplified

Wednesday, July 15, 2020

If you look around there are a lot of items you can measure 7 seconds


How does one system of measurement measure all this stuff?


The metric system can measure anything in the Universe.


Measurements have been a part of our lives for a long time.

In fact,  The first civilizations to record measurements were Egypt and Mesopotamia. In Egypt rods or bars of an exact length were kept in temples for basic measurement. The basic unit of length was the cubit, which was about the span from your middle finger to your elbow. 

However, there was a problem. Different countries or towns had their own unique measurements. For example, in Britain, you could measure mass using a slug, yes a slug, which was equal to about 32 pounds in the United States All of these different methods of measuring became very confusing and frustrating.

As a result, The International System of Units abbreviated SI was established in 1960 by the General Conference on Weights and Measures in order to create an international system of measurements

It is commonly referred to today as the metric system. Actually, the metric system has been around for much longer but for the most part the term “metric system” refers to a SI unit. 

First, the metric system is a decimal system. "Decimal-based" means all the units are based on powers of 10. Next, there are base units depending on what you are measuring and then this is combined with a system of prefixes.

Let’s begin with the fact that the metric system is decimal-based. For example, 30,000 centimeters equals 3,000 meters which equals 3 kilometers. So you are moving the decimal to the left or right depending on if the object you are measuring is large or small.  Why is this important? This makes conversion within the system easy.

Next, we are going to focus on base units and then prefixes.

Up first, the 7 base units. I call them the big 7 because the SI system is built around these units.

See the chart below


Name

Symbol

Measure

meter

m

Length

kilogram

kg

Mass

second

s

Time

ampere

A

Electric Current

kelvin

K

Thermodynamics temperature

mole

mol

Amount of substance

candela

cd

Luminous intensity


The next units are called the derived units. They use the base units in a formula. For example, the unit for area is a derived unit. In order to calculate the area you multiple length times width.

Therefore the unit is square meter It uses a base unit in a formula

Here is a partial list of derived units

There are 22 derived units


Name

Measure

Symbol

area

square meter

m^2

volume

cubic meter

m^3

luminance

candela per square meter

cd/m^2

speed velocity

meter per second

m/s^2

wave number

reciprocal meter

m^-1

acceleration

Meter per second squared

m/s^2

specific volume

Cubic meter per kilogram

m^3/kg

current density

ampere per square meter

A/m^2

amount of substance concentration

mole per cubic meter

mol/m^3

magnetic field strength

ampere per meter

A/m

mass fraction

Kilogram per Kilogram

kg/kg


Finally, there are accepted units.

For example, in almost any high school science lab you will measure volume using liters. A liter is an accepted unit that can be used with the SI units. In other words, it is accepted in most papers or journals but is not a base unit of the SI.

Here is a list of some accepted units



litre/ liter

L or l or

volume

Metric ton

t

mass

minute

min

time

hour

h

time

day

d

time

Astronomical unit

au

length

degree

°

plane angle

minute

plane angle

second

‘’

plane angle

hectare

ha

area


Next, you combine the units with prefixes.

Many of you have heard.

King Henry Died by Drinking Chocolate Milk


This is a mnemonic device used by people to remember several key prefixes of the metric system. ( See below)

Kilo Hecto Deka Base deci centi milli


These are examples of prefixes.

For example, if I’m measuring distance, the kilometer can be used for larger measurements like the distance across the state of Georgia or a millimeter can be used for small measurements because it is about the height of a credit card.

However, there are even bigger and smaller prefixes.

Here is a list of some but not all prefixes.


Prefix

Value

Magnitude

giga

1,000,000,000

109

mega

1,000,000

106

kilo

1,000

103

hecto

100

102

deka

10

101

BASE

1


deci

-10

10-1

centi

-100

10-2

milli

-1000

10-3

micro

-1,000,000

10-6

nano

-1000,000,000

10-9




Most of them are rarely used but the beauty is that you can take anything in the universe and there will be a prefix to measure it.

So in summary,

1. A base unit is a unit that you use based on what you are measuring,

2. Combine this with a prefix depending on the size.

3. Then everything is based on powers of 10


Related Links

Guide to Metric System


MooMooMath and Science


SI Units Measurement






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