Metric System of Measurement

The system of weights and measures may be a system of measuring. it's three main units:

m	-	the metre for length
kg	-	the kilogram for mass
s	-	the second for time

With those three simple measurements
we can measure nearly everything in the world! It's so easy.

Examples:-

Metre

The length of this guitar is
about 1 metre:
1 meter

When unfolded this ruler
measures 2 metres:

ruler

Kilogram

This gold bar has a mass
of 1 kilogram:-

1 kilogram

A dictionary also has a mass of
about 1 kilogram:-

Dictionary

Second

1 second is about as long as it takes
to say "one thousand and one"

Larger or Smaller ???

But what if we want to talk about big or small things?

Answer: we can use Metric Number Prefixes

like kilo
and milli
and so on

Examples:

something that is 1,000 metres is a "kilometre"

a very short time of one thousand th of a second is a "millisecond"

In fact the kilogram already uses this method, as it's a thousand grams, a kilogram.

Here is a quick summary of the special prefixes:

Common Big and Small Numbers

Name	The Number	Prefix	Symbol
trillion	1,000,000,000,000	tera	T
billion	1,000,000,000	giga	G
million	1,000,000	mega	M

Examples:

A thousand metres is a kilometre and abbreviated km (k for kilo, m for metre)

A million litres is a megalitre and abbreviated ML

A millionth of a second is a microsecond and abbreviated µs (µ is the greek symbol "mu")

We can also combine the metre, kilogram and second to make new Units of Measurement!

Example: Speed

Speed is how far something moves over a period of time

So it can be measured in metres per second

It means: How many metres does something travel in one second

We can write it as metres/second, or more simply m/s

Here are a few common units that are based on the metre, kilogram and second:

Volume:

Cubic Metre

Volume is length by length by length, so the basic unit of volume is a cube that is 1 metre on each side, in other words one cubic metre.

The Unit is metres × metres × metres, which is written m³

Litre

A cube that is 1 metre on each side is also equal to 1,000 litres.

1 m³ = 1,000 Litres

Litre is abbreviated L (some people use lowercase l, but that looks too much like 1).

So a litre is actually one-thousandth of a cubic metre.

Area

Square Metre

Area is length by length, so the basic unit of area is a square that is 1 metre on each side, in other words one square metre.

The Unit is metres × metres, which is written m²

Another way of thinking about a litre is:

A box that is 0.1 metres (10 cm) on each side,
One square metre that is millimetre thick.

Time

Hour

An hour is 60 minutes, and a minute is 60 seconds, so an hour is:

60 × 60 = 3,600 seconds

Day

A day is 24 hours so:

1 day = 24 × 60 × 60 = 86,400 second

Speed

Speed in metres per second (m/s)

This is a combination of two units (metres and seconds) to make a new one (m/s).

If something is moving at 1 m/s it moves 1 metre every second.

Speed in kilometres per hour (km/h)

A kilometre has 1000 metres, and an hour has 3600 seconds, so a kilometre per hour is:

1000 / 3600 = 1/3.6 = 0.277... m/s

How did I know to make it 1000/3600, and not 3600/1000 (the other way around)?

Acceleration

Acceleration is how fast velocity changes.

When a runner accelerates from 5 m/s (5 metre per second) to 6 m/s (6 metres per second) in just one second, they accelerate by 1 metre per second per second!

And yes, "per second" is used twice!
It can be thought of as (m/s)/s but is usually written m/s²

Force is usually measured in the Unit of Newtons, an important measurement in Physics and Engineering.Force

A Newton is how much force it takes to make 1 kg accelerate at 1 m/s².

1 Newton = 1 kg m/s² (one kilogram metre per second squared).

So force is actually based on the metre, kilogram and second.

So force is a combination of the three basic units.

SI

The Metric System had its beginnings back in 1670 by a mathematician called Gabriel Mouton.

The modern version, (since 1960) is correctly called "International System of Units" or "SI" (from the French "Système International").

So we should really call it "SI", but mostly people just call it "Metric".

A few special units are also needed to complete the SI System:

ampere for electric current,
kelvin for temperature,
mole for the amount of substance, and
candela for luminous intensity

complete list:

Quantity	Name	Symbol
Length	metre	m
Mass	kilogram	kg
Time	second	s

Electric Current	ampere	A
Temperature	kelvin	K
Amount of substance	mole	mol
Luminous intensity	candela	cd