http://www.unc.edu/~rowlett/units/index.html
Measurement in America
copyright © 2005 Russ Rowlett& the University of North Carolina at Chapel Hill.
Links for Metric History
Americans probably use a greater variety of units of measurement than anyone else in the entire world! We are caught in a slow-moving transition from the present units, customary, to metric units. ( http://www.unc.edu/~rowlett/units/custom.html) In fact, Americans employ a fascinating and sometimes frustrating mixture of units while talking about the same topics. For example, we measure the length of a race in meters, but the length of the long jump event in feet and inches! An engine's power is measured using horsepower and its displacement in liters. In the same dispatch, we describe a hurricane's wind speed in knots and its central pressure in millibars.
Metric Prefix
Equivalent number
Sci Notation
yotta- (Y-)
1 septillion
1024
zetta- (Z-)
1 sextillion
1021
exa- (E-)
1 quintillion
1018
peta- (P-)
1 quadrillion
1015
tera- (T-)
1 trillion
1012
giga- (G-)
1 billion
109
mega- (M-)
1 million
106
kilo- (k-)
1 thousand
103
hecto- (h-)
1 hundred
102
deka- (da-)**
1 ten
101
No Prefix
1
100
deci- (d-)
1 tenth
10-1
centi- (c-)
1 hundredth
10-2
milli- (m-)
1 thousandth
10-3
micro- (µ-)
1 millionth
10-6
nano- (n-)
1 billionth
10-9
pico- (p-)
1 trillionth
10-12
femto- (f-)
1 quadrillionth
10-15
atto- (a-)
1 quintillionth
10-18
zepto- (z-)
1 sextillionth
10-21
yocto- (y-)
1 septillionth
10-24
Furthermore, our English customary units do not form a consistent system. The measuring units used in America come from Celtic, Roman, Saxon, and Norse cultures. This mix is often confusing and contradictory. For example….
a. There are two systems for land measurement (one based on the yard and the other on the rod) and a third system for distances at sea, using nautical miles.Actually, only a few Americans know that the legal definitions of the English customary units are based on metric units! A yard equals exactly 0.9144 meter and an avoirdupois pound equals exactly 0.45359237 kilograms!b. There are two systems (avoirdupois and troy) for small weights and two more (based on the long and short tons) for large weights. Americans use two systems for volumes (one, ounces, for dry commodities and another, a different unit, but also called ounces, for liquids). The British use a third system. (British Imperial Measure). (btw: Did you know that the gallon, an English unit of volume, was originally the volume of eight pounds of wheat?)
Things are pretty confusing when it comes to measuring in America. The real challenge arises when Americans try to do science, engineering, and business with other countries. That's because most every country in the world uses the metric system! One bright spot, all scientists agreed long ago to use the metric system. However, US engineers and business people still haven't totally converted to using the metric system. This has led to many problems and accidents over the years. The excerpts in the news article below tells of a spectacular mix up
Mystery of Orbiter Crash Solved!
Kathy Sawyer Washington Post Friday, October 1, 1999; Page A1 NASA's Mars Climate Orbiter was lost in space last week because engineers failed to make a simple conversion from English units to metric units, an embarrassing lapse that sent the $125 million craft fatally close to the Martian surface, investigators said yesterday…..
It now appears this error had affected the orbiter mission from its launching almost 10 months and 416 million miles before its Sept. 23 failure. And yet the problem was never caught and corrected by the system of checks and balances at the Jet Propulsion Laboratory (JPL) in California, which manages this and numerous other interplanetary missions for NASA. As a result, flight controllers believe the spacecraft plowed into the Martian atmosphere, where the stresses crippled it, aborted its insertion into Martian orbit and most likely left it hurtling on through space in an orbit around the sun.
Mars Climate Orbiter
Baffled NASA officials said they were struggling to figure out how this happened, and bracing themselves for an onslaught of derision. "Our inability to recognize and correct this simple error has had major implications," said JPL director Edward Stone. The initial error was made by contractor Lockheed Martin Astronautics in Colorado, which, like the rest of the U.S. launch industry, traditionally uses English measurements. The Jet Propulsion Lab navigation team, on the other hand, uses metric measurements…..
Metric System Positives. The real beauty of the metric system is that there is only one fundamental unit defined for measuring each quantity. Ex: All Length measurements use the meter, Mass the kilogram (1000 grams) and Volume the liter. This makes it easy to measure, record and communicate data. (There are more fundamental units. Each is defined precisely in the International System of Units.)
Another real positive is that the metric system is based on Powers of Ten. Multiples and fractions of fundamental units are created by adjusting the decimal point and adding prefixes. The 6 original prefixes in this system were kilo- for 1,000, hecto- for 100, deka- for 10, deci- for 1/10, centi- for 1/100and milli- for 1/1,000. (King Hector Dunked Nothing Down Charlie's Mouth!)
Questions.
1. Tell what is both fascinating and frustrating about using the customary system of measurement.
2. Explain where the measuring units came from to create the customary system.
3. Describe the three measuring units used for length in the customary system.
4. Tell the two different systems for small weights and two for larger weights.
5. Do our customary units actually have metric equivalents? Give one example.
6. Explain why you think scientists around the world all agreed to us the metric system.
7. Explain briefly why the Mars Climate Orbiter became lost in space.
8. Tell two positives about the metric system.
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