Because MSC Software no longer sells Interactive Physics (they want you to buy the $10,000/year "Adams" suite), the software is now . While this occupies a legal gray area, for educational and archival purposes, the retro computing community has preserved it.
If you typed into a search bar, you are likely experiencing a very specific kind of nostalgia. You aren’t just looking for any physics simulator. You are looking for the first one. interactive physics 1989 updated download
This paper examines the history, educational impact, and modern availability of Interactive Physics Because MSC Software no longer sells Interactive Physics