On Jul 14 , at 8:47 PM, Pat Naughtin wrote:
I wonder if we will ever be ready to embrace the idea of using the
SI unit, metres per second, for speed in everyday conversations.
(using Australian examples):
School zone 40 km/h 10 m/s
Suburban street 60 km/h 15 m/s
Main (4 lane) cross town road 70 km/h 20 m/s
Highway 100 km/h 25 m/s
Freeway 110 km/h 30 m/s
There is a difficulty here that is not a problem with SI units; rather
it is a problem with
the time-of-day units, hours:minutes:seconds.
THIS IS THE PROBLEM
The difficulty arises because listing highway speed as 30 m/s does not
tell the driver what he/she needs to know. The driver is NOT
interested in how long it will take for his car to 30 metres; nor is
the driver interested in how far the car will go in one second. He
more likely needs to know something about the distance and time "to
Grandmother's house" or the like.
Since such distances are typically measured in kilometres (in metric),
one might try modifying the 30 m/s speed limit to 0.03 km/s but we are
now stuck with the awkwardness of a small number (fractional) and also
very short time interval (seconds) when a longer time interval (like
hours) seems preferable. (Perhaps we could use 3 km per 100 s, but I
find that to be awkward, too.)
My solution is to try to get rid of hours! (... and minutes.)
HERE IS A SOLUTION
(I am NOT proposing the adoption of this solution, only claiming that
a solution does exist.)
Without the hour, speeds could be conveniently measured in kilometres
per kilosecond.
Yes, 1 km/ks is identically equal to 1 m/s (so 30 km/ks is equal to 3
m/s), but it is in a form that is closer to what the driver needs to
know.
If Grandmother's house is 50 km away, then 30 km/ks will get him there
in a bit less than two kiloseconds. (If the driver has been accustomed
to measuring time of day in kiloseconds instead of hours, he will know
just how long that is.)
If he wants to know how far he will travel before lunch time when he
estimates that he/she wants to eat lunch in about 7 ks (about 2
hours), then he/she can easily see that he will be able to drive about
200 km before stopping for lunch.
The use of hours (and minutes) to measure time of day (clock time) is
the problem. SI works fine and has units of appropriate size for
anything, by using the right prefix. So we could use SI. We could
measure time of day in kiloseconds.*
RADICAL? Absolutely!
Practical? Yes, it could be.
Acceptable? Probably not.
CAN IT BE DONE?
Actually doing this would be difficult because it would be damned near
impossible to persuade people to give up the hour and minute for
measuring time of day. Therefore, I AM NOT SUGGESTING that we do this.
The only point I wish to make here is that the problem is NOT with SI.
The problem is with hours and minutes. Most of the world has accepted
SI metric which makes everything easier, except when we insist upon
clinging to the old non-SI, hours and minutes.
Let's make sure that people recognize that the problem with driving
speeds is NOT metric; the problem is hours.
Regards,
Bill Hooper
Fernandina Beach, Florida, USA
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*Additional explanation of how it would work for those of you who are
interested.
The kilosecond is 1000 seconds (of course) and is a convenient length
of time to measure time of day. It is about 17 minutes long, about a
third of an hour. Short time intervals of human activity would be
easily measured in a couple kiloseconds (like an hour's meeting which
would be 3 or 4 kiloseconds long). Intervals shorter than a kilosecond
could be measured in seconds (boil the pasta for 700 to 800 seconds).
Longer times during the day would not exceed the usual standard that
units should be used that keep numbers should between 1 and 1000;
actually, they would not even exceed 100, since there are 86.4
kiloseconds in a day. Note, that this scheme would have only one
additional time interval between the second and the day, namely the
kilosecond (as opposed to the present system of unnecessarily dividing
the length of the day into two additional subintervals, hours and
minutes).
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SImplification Begins With SI.
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