Wrong conversion between rpm and rad/s

[elaye]

Hello,

First of all thank you for this project, it's really useful and very well made!

I have an issue with the conversion between rpm and rad/s. When I try the following conversion 1 rad/s -> rpm numbat gives me 60 RPM even though it should output 9.5493. It seems there is a 2π factor missing according to the wikipedia article.

[sharkdp]

First of all thank you for this project, it's really useful and very well made!

Thank you for the feedback!

I have an issue with the conversion between rpm and rad/s

This is a common question that already came up a few times in the predecessor project. You might be interested in reading through those discussions (sharkdp/insect#187 or sharkdp/insect#50). The fundamental problem lies with the International system of units (SI), not with how it's defined in Numbat. The definition of rad and Hz in the SI lead to inconsistencies.

There is a way to resolve those inconsistencies, but it would require a change to the SI. Angles would need to have their own physical dimension. We actually do have support for this in Numbat, but it's currently only active on a feature branch. You can read (much) more about this here: #167 (see also the RPM example in the description). And you can try a (slightly outdated) version of Numbat with dimensionful angles here: https://numbat.dev/angles/. It will give you the correct answer that you expected.

[sharkdp]

@elaye Any feedback on this?

[elaye]

Thank you for your answer, that makes a lot of sense even though it's counter-intuitive!