Diminishing returns
If one worker is added to the third vacant sewing machine, output will go up by quite a bit (exponentially).
However, once we add workers after all sewing machines are taken, output will still go up. the fourth worker will cut the material, clean up, fill in for breaks. But output, while still going up, will increase in smaller and smaller increments.
give another scenario of diminishing returns?
Remember, capital and technology must remain constant. The only thing that is changing is labor.