Long and Short Run are terms that can be confusing from an economics perspective, as they are not based on a time dimension.
The Short Run is a period where at least one input is fixed (eg personell employed), and this is also known as the operating period.
The Long Run is a period where are inputs are seen to vary, and is also known as the planning horizon.
Diminishing Returns of Production
ASsuming that the firm is using all existing resources efficiently, then the extent to which the firm can alter its output depends on the extent to which the firm can vary its inputs.
The Law of Diminishing (Marginal) Returns
In the short run, when one or more factors are held fixed, there will come a point beyond which the additional output from using extra units of the variable inputs will diminish.
There will be an output beyond which the addition of units of variable factors such as labour, against a fixed input such as capital will result in a decline in output per employee. This is known as the Average Physical Product of labour.
Marginal Physical Product
This is the change in total output seen from employing each additional unit of variable factor input.
The Relationship between Production and Costs
The output at which the average cost per unit is at its lowest is known as the Technically Optimum Output.
The change seen in total costs of production as output is changed incrementally is referred to as the marginal cost. Where the total cost curve is linear, the marginal cost is constant, and it is easier to refer to this as the marginal cost of output.
The Incremental cost per unit is the total change in costs caused by the output increment. in other words the incremental cost equals the average marginal cost over the range of outputs.
Classification of Profits
Normal profits are made when profits ‘just’ cover the opportunity cost of investing this capital elsewhere. It is the minimum level of profits required for a firm to continue trading.
In incorporated companies this is equal to the ‘cost of capital’, which would include interest on loans and returns to investors.
In non-corporate entities this is the amount of profit required to persuade investors to invest money into a company to undertake production risks in an industry.
Supernormal Profit is seen to be all profit made above this normal profit.