Collapse of earth into underground mines, or subsidence, is a serious problem. In room-and-pillar and long-wall mines, columns of coal and other structures are used to support the ground above. Later in the mining process, they are often taken out. The mines are left to collapse.
We view overhead as two types of costs and define them as follows: Manufacturing overhead (also referred to as factory overhead, factory burden, and manufacturing support costs) refers to indirect factory-related costs that are incurred when a product is manufactured.
Variable manufacturing overhead costs will increase in total as output increases. An example is the cost of the electricity needed to operate the machines that cut and sew the denim. Another example is the cost of the manufacturing supplies (such as needles and thread) that increase when production increases.