# Boost Users :

Subject: [Boost-users] boost/units - converting forces (lbf->N)
From: Matt Vinson (matt.vinson_at_[hidden])
Date: 2018-12-01 19:03:40

Thanks for response....Yes, yes, yes.Â  I get that.Â  I am having trouble understanding the library; not force.Â  (Same as last time)
I guess I thought the library was magically accounting for gravity which is an error.
Updated:https://coliru.stacked-crooked.com/a/d256de6c16bdb08f
Thank you,

On Saturday, December 1, 2018, 9:10:38 AM CST, degski <degski_at_[hidden]> wrote:

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*.Â  Conversions between lengths are going well.Â  Conversion between forces are going well until pounds-force to newtons; line 182 in the link.Â  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 of one avoirdupois pound on the surface of Earth. Since the 18th century, the unit has been used in low-precision measurements, for which small changes in Earth's gravity (which varies from place to place by up to half a percent) can safely be neglected.[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

```--
â€œIf something cannot go on forever, it will stop" - Herbert Stein
```