marginal cost curve characteristics
Average costs are U-shaped, and the marginal cost curve intersects the average cost curves at their respective minimum points. In the competitive model of the firm, the minimum average variable cost is termed the shutdown point because a firm will not produce in the short run if price is below average variable cost.
The U-shape of the marginal cost curve is directly attributable to increasing, then decreasing marginal returns (and the law of diminishing marginal returns). As marginal product (and marginal returns) increases for relatively small output quantities, marginal cost declines.
The short-run marginal cost (MC) curve will at first decline and then will go up at some point, and will intersect the average total cost and average variable cost curves at their minimum points.