When I go to get a load of coal I’m assisted by a loader which looks a lot like this.
It’s impressive to see how much coal it can handle and how quickly I get the truck bed filled. The physics of how coal slides never really occurred to me until recently and I’ll pay more attention to it when I go back to the mine.
This reminds me that I keep saying “the mine” even though I learned that where I pick up my coal is just a crushing, sorting, distribution facility and the strip mine is actually several miles away. The coal it trucked to this site for processing.
I collect the coal I drag out of the coal bin chute into an antique coal bucket.also called a coal scuttle or hod. Now I notice that the shape closely approximates the 35º angle of repose of the contents. When the leading edge of the bucket is parallel to the floor the coal slides out.
Years before I ever heard the term, I observed the angle of repose in action as I watched antlions unwittingly exploit the tendency as they constructed and operated their conical ant traps. In the summer, I would lay near the house foundation on the south side where the soil was barren and powder dry. That was where the antlion eggs were laid and the larvae hatched and went to work catching ants.