The document discusses the downward slope of the aggregate demand (AD) curve and the upward slope of the aggregate supply (AS) curve in the short run. The AD curve slopes downward due to the real balance effect, interest rate effect, and foreign trade effect as price levels rise. The AS curve is horizontal at low output levels as unused resources allow expansion without cost increases. It slopes upward between potential and full employment as bottlenecks and declining marginal productivity cause costs to rise. The AS curve is vertical at full employment when no further output gains are possible. Short-run macroeconomic equilibrium occurs where the AD and AS curves intersect at an output and price level.