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The first step in being able to use imperial is to have the conversion factors from metric to imperial to hand, so questions
can be converted into the appropriate units. Please note the below conversion rates are rounded to a degree sufficiant for
most purposes, for the precise conversion rates go to www.google.com and type in the desired conversion, such as '1 Joule
in BTU'. This will work in most cases.
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Millimetres - inches
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/25.4
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metres - feet
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x3.281
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Kilometres - miles
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x0.621
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Litres - pints
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x1.76
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Millilitres - fluid ounces (UK)
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x0.035
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Kelvin - rankine
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/9 5ths
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Celsius - Fahrenheit
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/9 5ths, +32 (roughly double and add 30 for 20-100F)
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Kilogram - pound
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x2.205
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Gram - slug
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x0.000,068522
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Newton - pound force
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x0.225
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Newton - poundal
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x 7.2330
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Joule - BTU
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x0.00094782
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Joule - foot-pound-force
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x0.737562149277
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Joule - foot-poundal
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x23.7
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It is also helpful to know how to convert between imperial units. Although the numbers are not multiples of ten, this is no
harder to do than it is in metric (presuming in some cases you do have a calculator to hand, if you don't your computer will
have). To convert in the opposite direction to the conversions shown below (e.g. from feet to miles), just do the inverse
of what is shown.
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miles - feet
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x5,280, or x80, then x66
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miles - yards
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x1,760, or x80 then x22
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feet - inches
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x12
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yards - feet
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x3
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tons - pounds
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x2,240
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ounces - pounds
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/16
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fluid ounces - pints
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/20
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gallons - pints
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x8
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stones - pounds
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x14
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Feet/second - MPH
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/5280, then x60 twice
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A note for chemists: One fluid ounce (fl oz) of water at 62°F (521.67°R) weighs one ounce (oz) exactly.
Also, 1 gallon (gal) of water at 62°F (521.67°R) weighs 10 pounds (lb) exactly.
THE FPS SYSTEM
A slight variant on imperial which is better adapted to science and maths is the FPS system. This stands for Foot-Pound-Second,
and the system has been around for some considerable time. The system was designed to fit the essential science equation F=MA,
or force equals mass times acceleration. It does this by replacing the force unit PoundForce (lbf) with the Poundal (pdl).
One poundal is the force required to accelerate an object with one pound (lb) of mass at 1 foot per second per second (ft/s²).
The FPS equivalent to the Kelvin scale is the Rankine scale (°R). This uses the same degree as Fahrenheit, but starts
from absolute zero (-459.67°F).
Note: Alternatively, you can replace the weight unit, pound (lb) with a unit called the slug (sl). This is a matter of
personal choice, but in my opinion it is better to use the poundal for the sake of uniformity, as it is a little more frequently
used, and is better for physics as it is not limited to use on Earth's surface. Also, using the poundal does not upset the
fl oz - oz relationship (see above 'note for chemists').
ENERGY
The imperial unit of energy is the BTU, or British Thermal Unit, which is the energy required to raise the temperature
of a pound of water by one degree Fahrenheit. This is essentially the same function as the calorie serves in metric. In FPS,
you can also use the foot-pound-force or the foot-poundal, depending on whether you use the slug or poundal respectively.
These units are coherent, and fit physics equations.
A FEW PHYSICAL VALUES
Speed of sound: 1128 ft/s
Speed of light: 753,912,264 ft/s
Acceleration due to gravity: 32.15 ft/s²
Atmospheric pressure (ground level, Earth): 68087.256 pdl/ft²
Earth-Sun distance (1 Astronomical Unit): Approx. 93 million miles.
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