Today's Atlanta Journal-Constitution Question and Answer section by Colin
Bessonette included as the third question "How many gallons of water will
one inch of rain deposit on 100 square feet of land?" The answer given was
more than 62 gallons.
I would like to write to Colin Bessonette to show how much easier this would
have been had we as a society been using SI.
The square root of 100 ft� is 10 feet or 120 inches on a side. Thus 0.254
dm x 30.48 dm x 30.48 dm equals 235.9737216 dm� or 236 liters (to the
nearest litre). If the latter is multiplied by 0.264172052 by to get U.S.
gallons, one does get 62.3376622531 or 62 gallons (to the nearest U. S.
gallon).
The key to doing the problem with non-SI is knowing that one U.S. gallon has
231 cubic inches which I doubt one person in a thousand, (maybe one in 100
000) would know.
To do it that way one would multiply 1 inch x 120 in x120 in to get 14,400
square inches which divided by 231 equals 62.3376623376 gallons.
If I were to reword the question, would I want to say "How many litres of
water will one centimeter of rain deposit on 100 square metres of land?"
Then I would multiply .01 dm x 100 dm x 100 dm to get 1 000 dm� or 1 000
litres. Using decimeters seems the best to me since it is easy for everyone
to learn and remember that one litre is the same as 1 dm�.
Another way would be to multiply .01 metre x 10 metres x 10 metres to get
1.0 m� then move the decimal three places to the right to get 1 000 dm�
(because using decimetres of 1x1x1 equals 1 dm� or 1 litre).
Which approach would you all think would be best?
I think he will accept an email from me if I remind him that I sent him
information in early April about daylight saving time and then sent him the
question for which the answer was the information that I had just provided
to him.
Norm
