On 2007 Apr 23 , at 7:21 PM, Brian White wrote:
Har har. :) (pressure unit) kg/cm2. Typo.
On Mon, 23 Apr 2007 19:11:07 -0400, Pierre Abbat wrote
On Monday 23 April 2007 14:04, Brian White wrote:
I opened my Miata cluster to remove the L - H oil pressure gauge
for one
that read kg/cm3.
Both are technically wrong because they use the kilogram as a unit of
force. The unit of force in SI is the newton, not the kilogram. The
kilogram is a unit of mass in SI.
Yes, I understand that when someone refers to a kilogram of force
(kgf) they mean the weight of a kilogram of mass under "normal" gravity.
One pound of mass is defined as the mass whose weight force is 1
pound of force.
"Normal" gravity is 9.81 N/kg, so a pressure
of 1 kgf/cm^2 is 9.81 N/cm^2
which equals 9.81 x 10^4 N/m2
which is the same as 9.81 x 10^4 Pa (pascals)
and that is the same as 98.1 kPa (kilopascals)
We do the same when we use pound as both a force and a mass unit in
Ye Olde Enlgish mix of units. Either one leaves open the question of
what is "normal" gravity when we are measuring things in space, on
the moon, on Triton or Mars. etc.
However, the pound mass and the pound weight cannot be simultaneously
used to form a simple and coherent system of units, just as a
kilogram of mass and a kilogram of force cannot. In SI the kilogram
is ONLY a mass unit and the force unit is the newton.
Bill Hooper
1810 mm tall
Fernandina Beach, Florida, USA
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SImplification Begins With SI.
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