Total and Marginal Product for Trees

The left panel plots total product, the number of trees cut per hour, against the number of lumberjacks using one two-person saw. The right panel plots marginal product, the extra trees from one more lumberjack. The second lumberjack adds more than the first, six trees against four, because the saw works far better with two people on it.

From the third worker on, marginal product falls: a third can oil the saw or fetch water, a fourth adds one tree, a fifth adds nothing. This is the law of diminishing marginal product, and it comes from the fixed capital, the single saw. The sliders change what the second and third lumberjacks add, and the total product curve follows.