Why do we use two supply curves in the aggregate goods and services market? What is the difference between them, and why do they have different slopes?

Aggregate supply is divided into two supply curves because of the differing responses of domestic production to increase in the aggregate price level between the short and long run. The short-run aggregate supply's upward slope shows that firms can expand output in response to a rising price level only in the short run. The long-run aggregate supply's vertical shape shows that in the long run a country's production is limited by its resource base.