[question] Wrong unit conversion?

[rado84-github]

I think a screenshot would be better to explain the problem:

I chose N/m and yet the result shows something else, no Newtons per meter. What am I missing here?

[hanna-kn]

Pound is a mass unit in Qalculate, use lbf or PoundForce for the unit of force.

[davalden]

This question is actually a wrong question in the first place. The foot-pound is a measure of torque (twisting force) which converts to the metric unit of torque in newton-meters not newtons/meter (newtons per meter). However, it actually highlights a problem in qalculate - specifically the mis-categorization of units. Ever since Isaac Newton (the one for whom the metric unit of force is named) it has been understood that F = Ma where F is force, M is mass (a measure of the amount of matter) and a is acceleration (the change in velocity over time) and these are not interchangeable. Although it varies slightly from place to place, on the surface of our planet, a (often identified as little 'g' - as in g-force - the force of gravity on the earth's surface) is measured to be 9.80665 m/sec^2 or meters per second per second. This value in Imperial units converts to 32.174048556430446 ft/sec^2 or feet per second per second. Note that the second is the same in both measurement systems but the length unit is not. Qualculate correctly categorizes both the foot and the meter as length units. It fails, however, to correctly categorize the unit of mass and the unit of force in the Imperial system (often called FPS) as opposed to (MKS or CGS) in the metric system. The unit of force in the metric system is the newton (named after Isaac referenced above) and the unit of force in the Imperial system is the pound. The pound is thus mis-categorized in qualculate as a unit of mass and "Pound-force" is used instead. The unit of mass in the Imperial system is the slug (which doesn't appear at all in qualculate). This is a problem because qualculate has incorporated an impressive list of many units, commonly used or not, and to have a unit as fundamental as the Imperial unit of mass missing is a significant oversight. Furthermore, the Imperial unit of force (the pound) is in the list of mass units when it should be in the list of force units. Thus, using Newton's law and the numbers quoted above, one Kg (kilogram) has an average weight of 9.80665 newtons (Kg-meters/sec/sec) and one slug has an average weight of 32.17405 pounds (slug-feet/sec/sec) on our planet's surface. There is widespread confusion about this in the 21st Century and the global education system is to blame. One reason the metric system is preferred around the world is the kilogram is a better unit for measuring the substance of something than its weight. For example, astronauts/cosmonauts who spend time on the ISS (International Space Station) are essentially weightless (they weigh zero pounds or newtons) but their mass is much the same as it is here on our planet's surface. Mass doesn't change with location but weight does thus making mass a more reliable measurement of quantity. There is a constant of proportionality that can be computed for our planet's surface (and only on earth) between mass in kilograms and weight in pounds (2.2046 lb/kg) and this is often coded in measurement devices we frequently use (the bathroom scale). However, this does not imply (and this is the error that has been made) that the two units are in the same category. Thus, on the surface of the moon or on Mars it would be necessary to use a completely different scale because the acceleration due to gravity (a in Newton's 2nd law) there is significantly less than it is here on earth. However, as previously pointed out, an object's mass would be the same as it is here even though its weight would not thus, a scale used here on earth could be used to measure weight (newtons/pounds) there (the meaning of the measurement would, of course, be different) but its internal mass conversion would be completely wrong. There are, similarly, constants of proportionality between the Kg and the slug (14.5939029372046 Kg/slug) along with the newton and the pound (4.448221615255 newtons/pound) and these do not change with location because they are in the same categories. Conversion between mass and weight, however, do depend on location because they are not in the same category. This same error applies to ounces (not volumetric), Imperial tons and the pennyweight (which even has weight in its name). This approach could be used to distinguish between quantity measures as long as it is understood the location is on Earth's surface (we now live in a time when this is not necessarily the case). So, instead of "Pound-force" to mean "Pound," the quantity force-measures could be called Earth-ounce, Earth-pound, Earth-ton, etc. because they depend on being here on earth and are pretty much useless anywhere else. It will be interesting to see if this categorization error is fixed in future versions of qalculate (or, at the very least, the slug is added to the mass category). If it is to live up to its claim of "ultimate," qalculate needs to get the unit categorization right.

[hanna-kn]

@davalden

I do not care what some might perceive as more or less historically or physically correct. The only thing that matters, when it comes to units, is international (and national) standards, and agreed upon common definitions.