Ask A Scientist© Physics Archive

name         Jerome Gans
status       other
age          40s
       
Question -   What is a square newton? We have a carton whose sterngth
has been measured at 1020 KPA, with 1 KPA = 1 Sq Newton. We ultimately want
to convert this to square inch.
------------------------------------------------
Jerome,

    Something's wrong here.  The carton's crush strength is reported in kPa
(kiloPascal) which is a unit of pressure, the metric equivalent of pounds per
square inch.  A Pascal is 1 Newton per square meter.  A Newton is a unit of
mass while pounds are units of force so to convert between the two you have to
assume a gravitational acceleration (on earth, the acceleration is 9.8 m/s{2}
-- the bracketed number is a superscript, i.e., seconds squared.  In earth's
gravity 1 kg weighs 2.2 pounds.  Thus:

        1 kg X 9.8 m/s{2}   ~
        -------------------   =  4.45 N / lb
                2.2 lbs

    I'll leave it to you to convert square meters to sq inches.

Enjoy!

Greg
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Well, there can be such a thing as a square Newton, but the unit doesn't
make much sense.  Not as much sense, say, as a square second.  A Newton (N)
is a unit of force, like the pound.  (What is a square pound?)  Now, your
KPA is probably really a kPa, or kiloPascal.  A Pascal (Pa) is a unit of
pressure, and is equal to a Newton per square meter, N/(m^2) (this is a
fairly low pressure).  A kilopascal is 1000 Pa.  You can't convert this to
square inches, but you can convert to pounds per square inch.  A pound is
0.224 N, and an inch is 1/39.37 m.  So a square inch is (1/39.37)^2 m^2.
So a N/(m^2) = 0.224 lb / {(39.37)^2 in^2} = (0.224/1550)lb/in^2 =
0.0001445 lb/in^2 per Pascal.  A kiloPascal will be 1000 times this, or
0.1445 psi.


                Richard Barrans Jr., Ph.D.
=====================================================================
I have never heard of a square Newton.  I assume the KPA means kiloPascals.
A Pascal (1 KPa = 1000 Pa) is a measure of pressure (force per area), which
is equal to a Newton per square meter.  A Newton is a measure of force in
the metric system, whereas a pound (lb) is a measure of force in the English
system.  A square Newton would be the measure of a squared force, as to
which the physical meaning of it escapes me.  I thought most cartons gave a
measurement of how much pressure or how much force per area they could
handle.  Maybe converting the KPa to psi and then determine the square
inches you need for you cargo will give you the answer you want.  The
Machinery's Handbook has a large conversion table near the back of the book
to help you convert the pressures.  The last line of defense is to call the
manufacturer of the carton and ask them to explain it better.
I hope this helped.  Good luck.

Dr. C Murphy
========================================================================

I have never heard of square Newton.

Stress, strength, and pressure are type of quantities that are force per
unit area.  In the SI (metric) system, we use Newton (which is the unit of
force) per unit area (which is meter) to come up with N/m2 (read Newtons
per square meter) as the unit for pressure or stress.  Another name for
N/m2 is Pascal (abbreviated Pa).  (m2 means meter square).

In the English system the equivalent unit is pounds of force per unit area
in inch square.  This is denoted by psi (pounds per inch square)

By the way, k in kPa  means 1000 Pa. Also 1000 psi is denoted by 1 ksi.

An example: The atmospheric pressure at sea level is ROUGHLY 100,000 N/m2,
or 100,000 Pa, or just 100 kPa.  In the English system its value is 14.7 psi.

More precisely, to convert from kPa to psi, multiply the number by 0.145.
As for your example, 1020 kPa = 148 psi.

Good luck.


Dr. Ali Khounsary
Advanced Photon Source
Argonne National Laboratory
Argonne, IL 60439
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