Units. What are they? They are the means by which we measure how much of something we have got.
How far can this car go?
What time is it?
How much is a can of coke?
How much beer have I drunk tonight?
Knowing the answers to these questions enables us tell whether or not we can get there, late or not, have time to buy as many Coca-Cola's we need, how many beers I can safely consume before I go home, and how far it is to the nearest ReHab.
Of course, science has to be a little more exact than saying "a few", "enough, or "too many".
In fact, we have to be very precise about everything we measure.
The first example may be the simplest: Distance. How far away is that tree? The ancient civilisations used a "cubit",the distance from the tip of the fingers to the elbow of a regular guy.
Old England invented the "foot" consisting of twelve "inches". The "yard", being three "feet".
The trouble with these from a physics point of view was that there was no universal standard "foot" upon which everyone agreed.
The same applied to weight and the measurement of time.
After a nit of huffing and puffing (it was called the "cgs" system (centimeter - gram - second)), an international organisation called "SI" (Systeme Internationale) based in France, decided once and for all to actually define "length", "weight" and "time".
The Meter - the length of a platinum-Iridiumn bar in a lab at Sevres.
The Kilogram - a certain quantity of water (more in a minute).
The Second - 9,129,631,770 vibrations of a Caesium atom.
The history is fascinating. The thing about the decimal system is that all quantities are measured in multiples of ten, being prefixed by Latin words signifying how many tens:
Deca - 10
Kilo - 1,000
Mega - 1,000,000
Giga - 1,000,000,000
Tera - 1,000,000,000,000
and if you want to go smaller:
deci - 0.1
centi - 0.001
milli - 0.0001
micro - 0.000001
nano - 0.000000001
pico - 0.000000000001
femto - 0.000000000000000001
(This is just a selection of about 30 in all, but are the most common)
Doing a length conversion,
One "inch" was equal to about 2,54 centimeters
one "foot" was equal to about 1.5 decimeters.
The kilogram was deliberately defined to be the mass (weight) of exactly one cubic decimeter of water at 20 deg centigrade.
This was also defined as the "liter". However, it is not entirely exact. a cubic deciliter of water actually holds 1.0000028 (I forget how may zeroes) liters of water, due to an oversight in the definition, which remains ever since.
The meter was redefined as the length of the equator divided into 40,000 equal bits, and then re-redefined as a specific number of wavelengths of radiation from a specific atom. It was subsequently re-re-redefined as "the length of the path traveled by light in vacuum during the time interval of 1/299 792 458 of a second. ("299 792 458" is the number of meters light travels in one second in free space)
This system was first called the "MKS" system (Meter-Kilogram-Second),which was then revised to include units of electricity (the Amp) and energy (the Joule) amongst other things.
This system, which remains today, is called the SI system.
Simple, Innit?
Friday, May 08, 2009
Great Things are Afoot
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2 comments:
All measures are comparisons of one thing to another. Therefore, all measures are inexact. They are approximations to a particular goal.
Worse, the Metric System allows business to charge more for less through the trick of measurement using the Metric System. At least I think so.
That was the problem, we quantified it by as exact as the equipment measuring them. using stuff which never changed ie the atoms.
From that moment on, all measures wer only.
So you think that because you pay in dollars and cents (decimal (therefore metric) system) you pay more for stuff because the dollar is divided into 100 cents?
As ar as I know, apart from Korea and Japan, all monetary systems are by your reasoning ,charging you more. If they all charge you more, how do you know they are charging you more? Moer than what?
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