Rev.... 2002-11-01, 2003-05-01, -06-24, 2004-01-03, 2005-03-08, 2006-03-01, -08-15
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| Metric |
| Mixed |
| American |
| Electrical |
Comparisons are useful, even if approximate, so here are a bunch. At the Hardware Store, I use the estimate that a gallon is about 8 pounds when people are asking about hanging something from a nail or hook. Most people over-estimate the weight of things, saying something is "very heavy" which is relative to their strength (see Mixed).
Metric prefers that the units be used in multiples of 1,000 as in gram-kilogram although there are names for multiplying by 10 (deka-) and 100 (hecto-). Similarly, gram/milligram - divide by 1000 - centi- is by 100, and deci- by 10. Also, metric specifies in decimal fractions (0.25 rather than 1/4)
The world is justa'bout 40,000,000 meters around (40,000 km). This is not coincidence because the measure of the meter originally was to be one-ten-millionth of the distance from pole to equator through Paris. That total measurement was off, but the meter was taken to be the distance between two marks that were justa'bout that far apart.
Speed is measured in meters per second primarily, kilometers
per hour for cars and convenience.
10 mph = 14.67 ft per sec = 4.47 mps = 16.092 kmph
[note in certain old books, e.g. 1911 EB, m is used for miles]
100 km/hr = 62.14 mph therefore justa'bout the 55 mph speed limit
A person walking at a brisk pace can do a
kilometer in 10 minutes (therefore 0.1 km every minute) which is
6 km per hour
While in Thailand with the Army, when out on my own, I walked at this rate (3.73 mi/hr)
passing the tenth kilometer markers beside the road every minute to the second.
A centimeter is justa'bout the width of a man's finger.
A liter (of pure water) is exactly a kilogram, therefore a 2 liter bottle of soda is justa'bout 2 kilograms (4.4 pounds)
A tallish man of ordinary figure is justa'bout
100 kg. (220 pounds)
And is justa'bout 2 meters tall (6'6")
A Newton is the measure of force (as a kilogram is of mass) and is justa'bout a quarter of a pound [0.2248 lb, 3.5968 oz]
[American students live with the confusion of the pound being used for force and
mass - resistance to moving - because units were chosen to make them the same at
the surface of the earth.]
An inch is exactly 25.4 millimeters, by legal primary definition - the inch is not defined primarily by marks a bar somewhere although such bars exists as secondary definitions.
I find 4 - 2 liter (8 kg / 17.6 lb) bottles in a
paper bag comfortable to carry for a while with my arm wrapped
around them
while 2 - 2 liter bottles in a plastic bag (4 kg/ 8.8 lb) begin to
cut off circulation in my fingers walking them home from the
store.
When a person in the Store said a projection TV
set weighed 500 pounds, that it took 2 people to lift it, I
discounted that without arguing, but almost no one in the
ordinary world can lift 250 pounds - 100 pounds is a more
reasonable upper limit..
Most people find 30 pounds a reasonable lift if they don't have
to hold it too long, 60 pounds is very difficult. (bags of concrete mix are 60
or 80 pounds commonly.)
A common American red brick weighs about 4 pounds (1.8 kg). Overseas bricks are apparently heavier, an Australian site showing 3 kg as the lightest they sell.
The gram is the toughest unit for me to get a
grasp on. It is so small that there are nearly 30 in an ounce (28.35)
and I have some problems with ounces anyway. Most of us are
familiar with 1/4 pound (4 ounce) sticks of butter or margarine marked with
lines to divide off 8 tablespoons (a volume measure) so each mark
is 1/2 ounce or justa'bout 15 grams.
There are 16 tablespoons in a cup,
which if water weighs 1/2 pound/cup a tablespoon of water weighs
a 1/2 ounce (justa'bout 15 grams)
and a teaspoon weighs about 5 grams..
From: "Michael Miller" Subject: Trouble with your grams, still? Date:
Tuesday, March 08, 2005 2:17 PM
If you're still having difficulty grasping what a gram feels like, grab a
nickel. A nickel is a really good approximation of 5 grams.
Depending upon the
age/wear of the nickel, it'll be within +/- 2% of 5 grams. 2004-03-08
A "pint's a pound the world around", well not so much any more, but measure is still justa'bout right.
So, a gallon of milk is about 8 pounds, the weight of a newborn, for comparison with the weight of a picture for hanging on a hook.
3 teaspoons = 1 tablespoon; 16 tablespoons = 1 cup; 2 cups = 1
pint; 2 pints = 1 quart; 4 quarts = 1 gallon
Therefore 1 teaspoon justa'bout 2% of a cup (add oil to recipe to match whole
milk - 1t to cup 2% milk, 2t to cup skim)
1 tablespoon justa'bout 1.5% gallon (1/64th)
Because the voltage delivered by the power company varies depending on overall load - while the frequency remains rock solid - a 100 watt light bulb is justa'bout 1 amp (.833) and will have a resistance of justa'bout 100 ohms. (144)
An electrical element with 10 ohms resistance will deliver justa'bout 1200 watts from a nominal 115-125 VAC wall outlet. Wall outlets in houses and small businesses should be described as 120/240 as this is the middle of the range, although they are often said to be 120/220 or 115/230. The power company and regulators consider the voltage to be "wrong" only when it falls below 110 (a brown out) or above 130 (gag). Standard electrical appliance design requires "normal" operation to occur between 115 and 125 VAC. If the working or test voltage is given as 115 for rating purposes, the actual performance will justa'bout always be better than the rating. see electric.htm 2006-03-01
Low voltage is should be defined for safety purposes as below 30 volts because above this voltage, the normal resistance of the human body permits currents to flow that can stop the heart. Heavier insulation is required, circuit breakers, GFCI protection, etc. In NEC "Section 110-26(a) Exception No. 2, voltages of not greater than 30 volts ac and 42 volts dc are the dividing line." here The 24 volts used for a thermostat circuit is usually Class 2 wiring. The NEC does not require that thermostat wire or bell wire be installed in raceways , boxes, and auxiliary gutters etc. when these conductors are for Class 2 circuits as defined in Article 725