To apply the physics feature in Unity with Spine animations, ensure that you are using the correct version of the spine-unity runtime that supports physics. As of now, the spine-unity runtime does not fully support physics, but it is expected to be available soon. You might be encountering issues because the physics feature is not yet implemented in the spine-unity runtime for version 4.2. Additionally, make sure that your Unity project settings, such as the color space, are correctly configured, although this typically should not affect physics simulation directly. If the problem persists, consider checking for any updates or patches that might address this issue.