Many buyers and sellers each of whom has no influence on market price. Other things equal the higher is the price of the good, the lower is the quantity demanded. Sources of shifts in demand curves: prices of related goods, substitutes, complements. Shift in demand curve for ice cream cones: unusually hot summer, sharp drop in price of yogurt cones (substitute, law of upward-sloping supply. Other things equal, the higher is the price of a good, the higher is the quantity supplied. Source: firms seeking to maximize profits: market supply curve: sum of firm supply curves (assumes there is a large number of firms each of which can exert no influence on price. ) Movement along a supply curve versus a shift in the supply. A change in quantity supplied (as the price of the good changes) is a movement along the www. notesolution. com. A change in supply (for a given price) is a shift in the supply curve.