A moment ago I sent the following comment to the "contact us" link (via
query box) to the MathIsFun group, which runs a nice series of pages on
the metric system.
[quote]
I have looked at a few of your web pages on the SI and I am delighted
with most of what I see.
Your intentions on your weight versus mass page
http://www.mathsisfun.com/measure/weight-mass.html
are appreciated but you make some unfortunate mistakes.
First, weight is measured in newtons, not in kilograms. Weight is
calculated by multiplying mass (in kilograms) by the value for the local
acceleration due to gravity (in meters per second squared, about 9.8
m/s2). You can see that this results in the unit combination kg·m/s2
that you correctly cite for the definition of the newton. (I put the
exponent 2 on the line for the sake of non-HTML transmission.)
Secondly, in an elevator moving up or down at a constant speed, there is
no change in apparent weight. Only in accelerating elevators does
apparent weight change. The change in apparent weight is equal to the
mass times that acceleration. If the elevator is falling freely, it and
its occupants accelerate downward at 9.8 m/s2 and thus the occupant
feels as if he or she has lost all of their apparent weight and they
thus feel weightless. In short, this change in apparent weight depends
on the acceleration of the elevator, not that it is moving. Your web
page presents an Aristotelian (and incorrect) view of mechanics rather
than a Newtonian (and correct) view.
[end quote]
Jim
--
James R. Frysinger
632 Stony Point Mountain Road
Doyle, TN 38559-3030
(H) 931.657.3107
(C) 931.212.0267
