Weights And Measures

There are many different systems of weights and measures in use around the world, and it's often difficult to translate from one to another. Fortunately, the metric system is in use almost everywhere on Earth, and the American and Imperial systems are widely familiar. We shall use the SI metric system as our baseline, and provide conversions to the American and Imperial measurements, where it would be useful. The American and Imperial systems share the same weight and distance measurements, differing primarily in liquid measures.

The history of why the Imperial gallon differs from the US gallon is interesting. The Queen Anne (1707) wine gallon measured 231 cubic inches, yet the ale gallon most commonly in use (there were several) measured 282 cubic inches. When the Americans achieved independence in 1776 they had to adopt a system of weights and measures and chose to use the Queen Anne gallon for liquid measures. In contrast, the British chose to follow the ale gallon route when, in 1824, they defined the Imperial gallon as being that which contains 10 pounds avoirdupois of distilled water at 62 deg. Fahrenheit and barometer of 30 inches - a volume of 277.42 cubic inches. To further complicate matters, the Americans chose to have 16 fluid ounces (floz) in each of their pints, but the British chose to have 20. Oddly enough, this made the two fluid ounces almost identical!

We end up with the following conversion table:

Volume

US

Metric

Imperial

1 US gallon

3.785 liter

0.833 Imp gallon

1 US quart

946.35 ml

0.883 Imp quart

1 US pint

473.18 ml

0.833 Imp pint

1 US floz

29.57 ml

1.041 Imp floz

US

Metric

Imperial

33.81 US floz

1 liter

35.2 Imp floz

0.26 US gallon

1 liter

0.22 Imp gallon

1.06 US quart

1 liter

0.88 Imp quart

2.11 US pint

1 liter

1.76 Imp pint

US

Metric

Imperial

1.201 US gallon

4.546 liter

1 Imp gallon

1.201 US quart

1.137 liter

1 Imp quart

1.201 US Pint

568.26 ml

1 Imp pint

0.96 US floz

28.41 ml

1 Imp floz

Mass 1 ounce = 28.35 gram

1 pound = 453.6 gram

1 gram = 0.035 ounce

1 kilogram = 2.2 pound

Force It is important to distinguish between Mass and Force.

Mass is a physical property of material, a basic measure of how much "stuff' the material contains.

If you apply a Force to an object, it will accelerate. The more force, the greater the acceleration. The more mass the object has, the more force required to get the same acceleration. The amount of force required to accelerate 1 gram to a speed of 1 centimeter per second in one second is called a dyne, and the amount of force required to accelerate 1 kg to a speed of 1 meter per second in one second is called a Newton.

The Weight of an object is the force exerted on its mass by gravity. On the surface of the Earth, a 1kg mass sitting on a table exerts 1 kg-force downward. This force is what we measure as weight. Gravity accelerates objects to a speed of 9.8 meters per second in one second, so 1 kg-force is equal to 9.8 Newtons.

When objects are removed from gravity (eg on the space shuttle in orbit), they are weightless, but still have their mass. This is why astronauts handle large weightless objects so carefully - they take a lot of force to start moving, and just as much force to stop again.

Pressure Pressure is force per unit area. Measured in pounds per square inch, etc.

1 atmosphere = 14.7 lb/in2

= 760 mm of mercury (also called Torr) = 101.325 kilopascals = 1013.25 millibar

Length 1 inch = 2.54 centimeter

1 foot = 30.48 centimeter

1 centimeter = 0.39 inch

1 meter = 39.37 inch

Temperature Two things are important in temperature calculations: the actual temperature, and the difference or change in temperature.

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