1. Time Frame of Production
We talk about two basic time settings for production – the short run and the long run.

2. Production cost We will consider cost over two different time frames:
short run and
long run.
We will distinguish between two types of inputs:
variable and
fixed.

3. The input called capital
The main capital good of a firm is typically the plant or production facility.
It takes time to physically alter the plant so that the level of output can be changed.

4. Examples of plant adjustment
How long would it take to alter a restaurant facility?
6 months?
... to alter an automobile factory?
2 years?
Each production setting is likely to have a different time frame to alter the production facility.

5. The short run
The short run is that time period in which at least one input can not be changed or altered as output changes.
So, at least one input is fixed in the short run and the rest can be variable inputs.

6. The short run - continued
We typically think of the plant as the fixed input. The short run is that time frame right up to the time it takes to alter the plant.

7. The long run
The long run is the time frame longer or just as long as it takes to alter the plant.
Thus the long run is that time period in which all inputs are variable.

8. Costs
The short run means we have at least one fixed input and we have variable inputs (or maybe just one variable input). Thus, in the short run we will have fixed costs and variable costs.
In the long run we have only variable inputs. Thus, in the long run we will have only variable costs.