If a ppf has a negative slope and is bowed out, we experience opportunity costs as we continue to move down and to the right along the curve.

Explanation:

Production possibility frontier (ppf) is a graph which shows the existence of opportunity cost of moving from one combination of goods to another . Its slope is always negative and bowing out or downward sloping because opportunity costs always diminish or go down due to law of diminishing marginal return.

i might look it up later.