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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.


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.



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

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