Final answer:
Physical capital refers to plant and equipment while human capital refers to skills and knowledge of workers. Both types of capital can affect productivity.
Step-by-step explanation:
The category of physical capital includes the plant and equipment that firms use as well as things like roads (also called infrastructure). Physical capital can affect productivity in two ways: (1) an increase in the quantity of physical capital (for example, more computers of the same quality); and (2) an increase in the quality of physical capital (same number of computers but the computers are faster, and so on).
Human capital refers to the skills and knowledge that make workers productive. Human capital and physical capital accumulation are similar: In both cases, investment now pays off in higher productivity in the future.