Do all articles require a copyright form?

Yes. One of the authors must complete and submit the journal’s copyright form prior to acceptance. For articles published on a subscription basis, this generally transfers copyright in the article to IOP and/or its licensor(s) on acceptance of the article and for articles published on a gold open access basis in IOP journals, it gives IOP a non-exclusive licence to publish the article.  It also confirms various things, including that the work is original and that it is based on valid research.