TOMATO … TOMAHTO
Call it what you want
I said just call it what you want
Call it what you want
("Call It What You Want," by Foster the People, 2011)
"The time has come," the Walrus said, " to talk about the English and SI systems of measurement."
And we must talk about the English system of measurement because ...
Shout out to Burma and Liberia from the stubborn USA!
as the graphic to the right illustrates ...the good ole stubborn USA is one of the three remaining countries in the world that insist on using the English system industrially.
And since the PTOA is written in the USA its content will likewise continue to feature English units of measurement.
Fun Facts:
Sometimes the English system of measurement is called the "British Imperial System of measurement."
However, even the Brits have abandoned it and use the SI system of measurement!
Ergo, the blame for the English system of measurement is sometimes pinned on the USA via renaming it the "United States Customary Units of Measurement."
Tomato ... Tomahto.
The SI system of measurement also has its own inherent confusion.
Let's start with the phrase "SI system" which literally translates into the redundant phrase "System International system" of measurement.
Furthermore, the SI system of measurement has basically adopted the vast majority of the metric system of measurement.
Kind of crazy that something as fundamental as how stuff is measured has to start off from the get-go being so confusing, eh?
"SI system" is also the "metric system"...
"English" versus "British Imperial" versus "American Customary Units of Measurement" ...
The important distinction to make is that the term chosen to describe a measuring system is no big deal ...
However ...
Recognizing when to apply the appropriate conversion factor between the two is crucial!
No joke!
In 1999, the $193 million dollar Mars Climate Observer was lost because the USA firm that built the space traveler failed to convert the thruster calculations from English to SI units.
The advent of globalization has also meant that machinery and tools built with metric tolerances and fasteners are now commonly available in the United States.
Conversion factors are used to convert between the SI system of measurement and their English/British/US Customary unit equivalents.
A list of important conversion factors that has helped Your Mentor convert between English and SI measuring units while traveling around the world appears at the end of this PTOA Segment.
EXAMPLES OF ENGLISH AND SYSTEM INTERNATIONAL (SI)
MEASURING UNITS
Force Measurement
Who amongst us by now doesn't recognize the following mathematical expression for a gravity-caused "Force"?
F = mass * g
And in the event you seriously don't know then you need to return to PTOA Segment #142 pronto!
Otherwise ...
PTOA Readers and Students who are reading the PTOA Segments in the intended sequential order already know that ... in English units ...
1 pound of force (lbf) is created by and therefore equal to ...
1 pound of mass (lbm) multiplied by the acceleration of gravity (g) ...
and the acceleration of gravity in English units is 32.2 ft/s2.
In SI measurement lingo the unit of force is the Newton (N) ...
which all PTOA Readers and Students have learned is created by and equal to a 1 kilogram of mass times the acceleration of gravity ...
and that the acceleration of gravity in SI units is 9.8 meters/sec2.
Note, however ... that an SI Tomato is not an English Tomahto!
1 N ≠ 1 lbf!
There are 4.45 Newtons in 1 lbf.
Gee whiz!
A Newton is quite a bit smaller than a psi because it takes 4.45 of them to equal 1 lbf.
Otherwise stated:
4.45 N = 1 lbf
Dividing each side by 1 lbf :
4.45 N / 1 lbf = 1!
Did you notice?
A conversion factor is simply a ratio of two equal things that ... when divided by each other ... equals 1!
Pressure Measurement
Who amongst us by now doesn't recognize the following mathematical expression for "Pressure" which is created and defined by a Force distributed over an Area?
P= F/A
In SI units ...
the PV Pressure is measured in Pascals ...
1 Pa = 1 Newton divided by a square meter = 1 N /m2
In English units, the PV Pressure is measured in "pounds of force (lbf) divided by square inches" ...
1 psi = 1 lbf divided by 1 square inch = 1 lbf / in2
However ... there is not a one-to-one correspondence between the two:
1 Pa ≠ 1 psi!
Actually it takes 6894.7 Pa to equal one psi.
Otherwise stated:
6894.7 Pa = 1 psi
Yikes!
6894.7 is a big number!
Let's make it more manageable to work with Pascals by dividing by 1000!
6.895 kPa = 1 psi
and thus if follows that:
6.895 kPa / 1 psi = 1
Once again, a conversion factor is simply a ratio that equals 1!
And that is why conversion factors can easily translate one measurement system into another.
PTOA'S HANDY DANDY TABLE OF CONVERSION FACTORS
In this day and age Your Mentor does not expect PTOA Readers and Students to actually use the PTOA Handy Dandy Conversion Factor Table below.
Your Mentor expects PTOA Readers and Students to glance over the table to acquire a relative sense of how much bigger one part of the conversion is compared to the other.
For example:
"3.79 liters / gallon" means that it takes 3.79 liters to fill up one gallon.
and the flip-flop inverse story of the above conversion factor is as follows:
"1 gallon / 3.79 liters" means that it takes only 0.264 gallon to fill up one liter!
After understanding the magnitude of the forward and inverse relationship of conversion factors, Your Mentor expects PTOA Readers and Students to use one of many online conversion factor tools.
One all-purpose online tool is the GOOGLE CONVERSION TOOL.
The Google Conversion Tool allows you to toggle the Upper Bar Menu for a variety of measurements types (for example Mass, Length, Volume, Force, Pressure, Energy, Temperature). Then the lower two bars can be toggled to perform the desired conversion.
If you don't have access to Google, the following PTOA Handy Dandy Conversion Factor Table will include most of the conversions applied in the PTOA.
PTOA'S HANDY DANDY CONVERSION FACTOR TABLE
| FACTOR | UNITS OF CONVERSION | Type of Conversion |
| 2.54 | Centimeter (cm) / inch (in) | Length to Length |
| 39.37 | Inches / Meter | Length to Length |
| 0.305 | Meters (M) / Foot (ft) | Length To Length |
| 5280 | Feet / Mile | Length to Length |
| 1609 | Meter / Mile | Length to Length |
| 231 | Cubic Inches(in3) / Gallon (gal) | Volume to Volume |
| 35.31 | Cubic Feet(ft3) / cubic meter(M3) | Volume to-Volume |
| 3.79 | Liter (L) / Gal (g) | Volume to Volume |
| 28.316 | Liter (L) / Cubic Foot (ft3) | Volume to Volume |
| 1000 | Liter (L) / Cubic Meters (M3) | Volume to Volume |
| 264.2 | USA gallons (gal) / cubic Meters (M3) | Volume to Volume |
| 42 | USA gallons (gal) / USA barrel (bbl) | Volume to Volume |
| 454 | Grams(g) / Pound of Mass (lbm) | Mass to Mass |
| 2.2046 | Pound of Mass (lbm) / Kilogram | Mass to Mass |
| 2000 | Pound of Mass (lbm/) / US short ton | Mass to Mass |
| 2240 | Pound of Mass (lbm) / British long ton | Mass to Mass |
| 2204.6 | Pound of Mass (lbm) / Metric Tonne | Mass to Mass |
| 1000 | Kilograms / Metric Tonne | Mass to Mass |
| 62.4 | Lbm H20 / cubic foot (ft3) | Density of water used as conversion factor to swap between mass and volume of water. Application of liquid specific gravity makes it possible to apply conversion calculation to any liquid |
| 8.34 | Lbm H20 / gal | Density of water used as conversion factor to swap between mass and volume of water. Application of liquid specific gravity makes it possible to apply conversion calculation to any liquid. |
| 0.0765 | Lbm Air / cubic foot (ft3) | Density of air at 59 deg F used to convert between mass and volume of air. Application of gas specific gravity makes it possible to apply conversion calculation to any gas. |
| 4.45 | Newtons (N) / Lbf | Force to Force |
| 6894.7 | Pascals (Pa) / Psi | Pressure to Pressure |
| 6.895 | KiloPascal (kPa) / Psi | Pressure to Pressure |
| 14.7 | Psi / Atmosphere(Atm) | Pressure to Pressure |
| 760 | mm Mercury (mmHg) / Atm | Pressure to Pressure |
| 29.92 | inches Mercury (inHg) / Atm | Pressure to Pressure |
| 777 | Foot-lbf / BTU | Mechanical Work to Energy |
| 1055 | Joules / BTU | Thermal Energy SI to Thermal Energy English |
| 252 | Gram-calorie / BTU | Calorimeter Energy to English Thermal Energy |
| 2545 | BTU / hp hr | English Thermal Energy to Work Energy Done in One Hour |
| 3412 | BTU / kwh hr | English Thermal Energy to Electrical Power Consumed by Generating 1000 Watts Electrical Energy for 1 hour |
| 550 | Foot lbf /second horsepower (hp-s) | Mechanical Work/Energy performed in 1 second to Power Conversion |
| 33000 | Foot lbf / min hp (hp-min) | Mechanical Work/Energy performed in 1 minute to Power Conversion |
| 0.745 | Kilowatt / horsepower (hp) | Electrical Power to Engine Power Conversion |
TAKE HOME MESSAGES: Since there are no plans for the USA to move to the SI system of measurement, PTOA Readers and Students must be aware of and able to convert between the English and SI systems of measurement.
Conversion factors are used to convert between the two systems.
Conversion factors relate how much quantity of one factor ("A")will equal the amount of one unit of the other factor ("B").
Conversion factors tell two stories!
The inverse conversion factor can also be used to determine how much "B" will equal "A."
©2016 PTOA Segment 0148
PTOA Process Variable Pressure Focus Study Area
PTOA Introduction to PV Pressure Focus Study
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