search

openwebwork / pg

Problem rendering engine for WeBWorK
http://webwork.maa.org/wiki/Category:Authors
Other
45 stars 76 forks source link

Error in units: lbf is not a foot-pound, ft-lb is. #504

Open drgrice1 opened 4 years ago

drgrice1 commented 4 years ago

There is a mistake in the units in webwork. The units that are listed when helpLink("units") is used in a problem, list a foot-pound as having the abreviation lbf. That is invalid. An lbf is an abbreviation for a pound-force, which is not a foot-pound. Essentially it is the same as a pound, but with the emphasis on it being a force, and not a mass. The problem is also in the definitions of the units themselves in pg/lib/Units.pm.

Alex-Jordan commented 4 years ago

An old related thread: https://webwork.maa.org/moodle/mod/forum/discuss.php?d=4035

I remember when this happened, I was visiting family over winter break. Things happened that dropped this issue from my radar, and I never followed through with the pull request mentioned at the end of the thread.

drgrice1 commented 4 years ago

Perhaps you could follow through with that pull request now? This does seem to affect quite a few problems in the OPL, and those will all have to fixed. It might take some work.

Alex-Jordan commented 4 years ago

I might, but I am short on time this week. I would also like to consider if there is any effect on this from the added feature of creating your own units, which was not possible back in 2016. Probably not, but

Alex-Jordan commented 4 years ago

Errant click. I was saying...

Probably not, but I'd like to think about that. Does anything occur to you?

drgrice1 commented 4 years ago

I can't think of any adverse effects that could be created by adding your own units. Unless someone was counting on an invalid conversion between lbf and other units.

drgrice1 commented 4 years ago

On another note, the foot-pound conversion factor's accuracy could be improved. Currently the conversion factor is set to 1.35582. Answers for work that come up in problems can become quite large, frequently in the hundreds of thousands if not millions, and that is not sufficient for the conversion with any decent accuracy. In a quick search I was able to find a conversion factor of 1.3558179483314004 with much better accuracy.

Edit: The factor I Google searched above is exactly what you get if you use the product of the conversion factors in Units.pm for a foot (0.3048) and a pound (4.4482216152605).