Re: [Boost-users] boost/units - converting forces (lbf->N)

Subject: Re: [Boost-users] boost/units - converting forces (lbf->N)
From: degski (degski_at_[hidden])
Date: 2018-12-01 15:10:25

On Sat, 1 Dec 2018 at 15:26, Matt Vinson via Boost-users <
boost-users_at_[hidden]> wrote:

> To see if I understand the library, I want to create metric and imperial
> systems without using Boost Units predefined systems*.  Conversions
> between lengths are going well.  Conversion between forces are going well
> until pounds-force to newtons; line 182 in the link.  What am I doing wrong
> when lbf will not convert to newtons?
>

Gravity is not your friend [and gets in the way of what you want to do],
you're not doing anything wrong [C++-wise], but you're converting
hamburgers to cheeseburgers [for free], they don't convert.

>From Wikipedia (https://en.wikipedia.org/wiki/Pound_(force)):

The pound-force is equal to the gravitational force exerted on a mass
<https://en.wikipedia.org/wiki/Mass> of one avoirdupois pound
<https://en.wikipedia.org/wiki/Pound_(mass)#Avoirdupois_pound> on the
surface of Earth <https://en.wikipedia.org/wiki/Earth>. Since the 18th
century, the unit has been used in low-precision measurements, for which
small changes in Earth's gravity
<https://en.wikipedia.org/wiki/Gravity_of_Earth> (which varies from place
to place by up to half a percent) can safely be neglected.[4]
<https://en.wikipedia.org/wiki/Pound_(force)#cite_note-4>

The 20th century, however, brought the need for a more precise definition.
A standardized value for acceleration due to gravity was therefore needed.
degski
-- 
*“If something cannot go on forever, it will stop" - Herbert Stein*