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The Metric System

Physics Honors: Assignment- 1 introduction "Prove It"

Patrick Patterson

on 9 December 2014

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Transcript of The Metric System

273.15 is essentially the number that connects the Kelvin and Celsius scales so well.
The International System Of Units
The Metric System
"The Metric System" is now a colloquial synonym and essentially has been since 1960.
That is when the International System of Units -- the modern form of The Metric System -- was officially established.
Though, the abbreviation "SI" is derived from the orginal term developed by the French; Le Système international d'unités, or...
Now, there are some different components to this system; the first of which being...
Base Units
Base Units, as the name suggests, construct the basis for SI.
There are seven to fill the measurement roles holes...
Electric current
and luminosity.
And mass.
Each of these has its own respective unit of measurement within the SI.
It should also be mentioned that the French have had a large influence with the Metric System.
They were the first to introduce it in during the late 18th century.
That's when the French Revolution occurred.

Prior to which, France had an estimated quarter of a million different units of measure.
The Revolutionary government began to establish a standard system based upon five units of measure.
The introduction was poorly managed, but in 1812, Napoleon declared it law to utilize the metric system and it was continually tought and refined for many years.
Napoleon was also an integral part of introducing the Metric System to the world during his expansion of the French Empire in the early 19th century.
And though some reverted to their previous systems of measurements, many retained the Metric System.
With so many Nations now adopting the Metric System, it was important to confirm the units of measure across all that used the system.
This lead to the Metre Convention in 1875; an international treaty that instituted the formation of three organizations to maintain the Metric System.
International Bureau of Weights and Measures (BIPM
<French abbreviation>
); used to maintain the measurements.
General Conference on Weights and Measures (CGPM); an every four to six years meeting among nations.
International Committee for Weights and Measures (CIPM); a supervisory committee that meets with BIPM.
This would eventually lead to the formation of SI at the 11th CGPM in 1960.
But enough about history, on to the system.
The amount of substance.
Ampere for electric current.
Kelvin for temperature.
Candela for Luminosity.
Metre (meter) for length.
Second for time.
Mole for amount of substance.
Kilogram for mass.
The "Ampere" measures electric current such as the one spewing out of atmospheric jets and quasars at galactic cores.
It's official definition is, "the constant current that will produce an attractive force of 2 × 10^–7 newton per metre of length between two straight, parallel conductors of infinite length and negligible circular cross section placed one metre apart in a vacuum."
Sounds complicated, but essentially 1 amp (as it is commonly abbreviated) is the rate at which 6.241 × 10^18 electrons (that's quintillions of electrons) travel past a given point on an electric circuit per a unit of time.
So, simply it is really the rate of flow by those electrons.
It is commonly employed with the Second to form the SI derived unit for electric charge of 1 Coulomb = 1 amp x 1 second (charge carried by 1 amp per second).
Here is a visual aid to help explain things better.
Interestingly enough, the largest electric current ever discovered was found near galaxy 3C303 which has such jets at its heart.

It was recorded as 10^18 amps; that is about 1 trillion lightning bolts going off simultaneously and it has likely maintained this force for quite sometime!
Not to be confused with Derived Units, the second part, which would only be done as simply classification confusion.
Derived Units are really just the offspring of multiple base (and in some cases, other derived) units creating a physical equation to express a measurement value such as electric charge, volume, and density.

Take a common one like velocity shown as M/S. Its equation is: Meters x S^-1 (Seconds); utilizing the base units of meters and seconds in order to possess a unit of the rate of travel.
20 of them are incorporated, they increase the unit (be it base or derived) by a factor of ten with each subsequent prefix and same in reverse. Some are much more common then others.

This is where the key simplicity of the system is housed.
The third component is prefixes.
Temperature is recorded as Kelvins.
The Kelvin scale is defined upon two areas.
1. "0" on the scale is absolute zero, this is the point in thermodynamic temperature during which matter has the least movement and can become no colder; making Kelvin an absolute scale.

And 2. The triple point of water; the instance during which the three phases of a substance (gas, liquid, solid) are in a state of balance. This is measured at 273.16 degrees kelvin.
-273.15 degrees Celsius is absolute zero on that scale. Hence the easy conversion of adding or subtracting from the scales to receive conversions.
On the Celsius scale, "0" is defined as the freezing point of water, where as its triple point is 0.01 degrees.
The scale was named after Lord Kelvin (William Thomson).
An engineer and physicist, Kelvin discovered absolute zero on the Celsius scale.
A nice 65 degrees Fahrenheit is 291 K! Sounds hot to us.
This guys surface -- 5778 K
Here is another visual aid.
Practically every country but a mere few use Celsius as a day-to-day temperature scale that is only overshadowed in very particular fields by Kelvin.
The 13th CGPM authorized the official use of Kelvin and Celsius in tandem.

Many scientists make use of both scales simultaneously do to the simplistic conversion method and widespread of Celsius.

As well, Celsius being expressed in fewer numbers (at low levels) is easier to comprehend.
The Candela
This is one of the more obsucure units (among the average person).
It covers luminosity intensity...
Or the power generated in a certain direction as determined by the luminosity function, a standardized model of the average human sensitivity to the visual perception of brightness measured in wavelengths.
The typical candle produces light at the grade of about one candela.
Candela is Latin for candle.
The Candela as defined by the 16th CGPM is...
"...the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity in that direction of 1⁄683 watt per steradian."
Though it is defined in terms of the Steradian, the Candela remains a base unit by definition.
It also shares a relationship with the two SI derived units, Lumens and the Lux.
Not very bright.
The sun is about 20 sextillion (21 zeros) candelas.
Distinguishing the difference between the three can be some trouble.
Candelas account for the
of a light at its source in a given direction.
Lumens are the measure of
light is produced regardless of its distribution.
A Lux is used to determine the proficiency of
an object is illuminated as determined by its distance.
So say you have a flashlight that emits 100 lumens at 100 lux...
Now decrease the diameter of its spread (concentrate the beam) on the surface it is shining to 1/10 of its original size, and now it is 100 lumens still, but at 1000 lux. The same applies with one's proximity to the surface; move farther away, the lux depreciates, move closer and it intensifies.

The Candela power will remain constant so long as the beam is not obstructed from the intended object it is illuminating.
This is a video explanation of Lumens; it may not be Candelas, but it is another comprehension tool.
Length in Meters
The original definition of the Meter was one ten-millionth of the distance from the Earth's equator to the North Pole (at sea level).
It remained essentially the same standard and was simply refined and its precision ameliorated until it was put on the Krypton Standard or, "...equal to 1650763.73 wavelengths in vacuum of the radiation corresponding to the transition between the levels 2p10 and 5d5 of the krypton 86 atom."
This standard, however, had some issues and was eventually replaced by the Speed of light standard.
In 1960, the elventh CGPM defined the orginal SI system with the meter as measured in wavelengths, that same year the laser was developed.
And in 1975 the conventional definition of the speed of light was defined. And in 1983 at the 17th CGPM, the Meter was defined as "the length of the path traveled by light in vacuum during a time interval of 1⁄299,792,458 of a second."
Here is some historical and comprehension material.
To the topic of the United States customary units Vs. the Metric System, it's no contest for the simple reason displayed here.
The down right bizarre derivatives of the units is what makes them so incredibly complex. The imperial system also does not make use of prefixes, it has individual names for each subsequent value.

Thus, this is all that is ever mentioned between the two systems. The fact of the matter is that the imperial system is simply too inconsistent to be widespread or comprehended sufficiently.
Now, when it comes to larger measurements, the meter is paired commonly with the prefix kilo to create kilometers (1000 meters to 1 Km).
To add some perspective...
The diameter (at the equator) of the Earth is 12,756.1 km or 12756100m.
The average distance between Luna and the Earth is 384,403.1 km or 384403100m.
As one can observe, among the vastness of space, these units become fairly impractical, and even the use of much higher prefixes is frowned upon.
So the BIPM's recommended unit for astronomical measurements is the au (Astronomical Unit).
That is the average distance between Earth and the sun.
1 au is equal to 149,669,180 km.
And even that unit is fairly impractical on a galactic scale; on a universal one, it is even more unsuitable.
From our blue marble...


3C303, is an astonishing 126,479,343,400,000 quadrillion au.

That is 2 billion light years!
Which comes from the distance light travels in a single year and brings us to our next topic.
Even on a star scale, km are fairly incomprehensible.
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