Characteristic Effects
Not every repeated activity manifests itself physically. But every physical thing is a manifestation of repeated activities.
Every thing is characterized by its activities. These activities, constantly recurring, constitute the thing, they make up its appearances, letting it multiply. The typical effects these activities have on other things indicate the existence of the causing thing.
If there are such characteristic effects, recurring, forming a noticeable pattern, then there is a thing. If the effects are in accordance with certain rules (some of them called “laws of physics”), then the origin of the effects is a physical object.