On The Phenomenology of Spirit (1807), ch. 3, "Force and the Understanding." What is "force" as physics describes it? And scientific law? Do these terms denote objects in the world, or models for how we describe the world?
For Hegel, force is a way of talking about the metaphysical relation that one object has to other objects. Or taken from another perspective, it's the relations themselves that become objects for our understanding of the world. Hegel's position is a variation on Hume's account of causality, which said that causality is not a matter of one object in the world exerting some hidden power on another object in the world, but instead a pattern of always seeing one kind of thing (which we call effect) happen after another kind of thing (which we call cause). For Hegel, likewise, talking about force is a way of talking about how certain happenings strike us as always related to other happenings, such that a magnet, for instance, is defined by its having effects on metals and other magnets.
More generally, Hegel develops the concept of force as a solution for how to describe how objects are individuated from each other at all. As discussed in our previous episode, if you say that an object is what it is because of its properties, that seems to undermine the unified character of that object: It becomes just a bundle of properties. By thinking instead of the relations between objects (i.e. extrinsic properties), we can consider each object as unified (as a One), but individuated by their position in a pattern of objects, or rather a pattern of events that involve (and so essentially create) these objects.
Grasping such a pattern requires the Understanding, i.e. abstract, conceptual thinking not tied closely to particular perceptions. We're not merely saying "this red I'm perceiving now is what it is because it is different from white and the other colors, and it's a color in that it's not a shape or texture or other sensory modality" to individuate a sensory property. We're going beyond this and explaining that color is a result of light of various wavelengths striking objects and hitting eyeballs, such that we can systematically say what the relation of colors are to each other and to other properties an object might have. A color becomes an action, an event. Something is impressing (forcing) its color onto my perception, and there are many force interactions in this grand pattern that don't result in perceptions at all, such that we can call the concepts involved "unconditioned universals," because the concepts aren't "conditioned" by our sensory apparatus. While of course we often see (or otherwise sense) the results of force (and wouldn't be talking about it at all were it not for our sensory experience), it us not like a particular patch of red or a particular sound but instead a general schema or theory about the interaction among the world's elements.
As this chapter proceeds, we move from talking about force (the individual relationships in this pattern) to talking about natural law (as a way of making generalizations about the pattern, and also as a way to refer to the pattern as a whole, i.e. the Law of Nature that makes everything move the way it does, to finally putting this back on the Understanding per Hegel as idealist: This pattern is not just something in nature, but something in the mind, because there's no sharp dividing line between nature and mind. Yes, as we discussed last time, we can be wrong about particular things in nature, but that's only because we're misaligning concepts (thinking that the pencil in water really is bent without understanding the forces that make it merely look bent), when the concepts and so the way we would resolve these illusions (taking the pencil out of the water and putting it back in until we've figured out the physical laws involved) are all ultimately furniture of our minds.
So the idea that there is a Kantian "thing-in-itself," an inner nature of the experienced world that is forever beyond our experience, is actually a part of experience. The pattern presents itself as having depths, but of course with science, we peel into those depths and do, for instance, describe the inner workings of light and shape that account for the visible patterns of colors. But even as we do this, that explanation presents itself as having further depths that we don't yet understand. While for Kant, scientific discoveries are all within that veil of phenomena that forever lies over the true, inner world, for Hegel, the world presents itself as more like an onion with no inner layer at all, just more depths for us to potentially plumb. So saying that this is "all in our minds" is not to say we all just make it up like a dream, but that we only have experience insofar as we're creating structure, and it's this structure that science investigates. To further understand how this might work, we'd have to reflect our own minds, on self-consciousness and how it is in turn formed by social forces, which is exactly what the subsequent chapters of the book explore.
Start at the beginning of our treatment of this book with ep. 275.