These pictures are called demand curves . Price is put on the vertical axis and quantity on the horizontal axis. Demand curves slope down from left to right. When one of the determinants of demand changes, the demand curve shifts to the left or the right. Supply is the quantity of a good or service that sellers are willing and able to offer for sale at various prices.
People often confuse supply with quantity supplied .
Supply refers to a list of quantities and prices. Quantity supplied is the amount of a good or service that people are willing and able to offer for sale at one specific price. When economists construct a supply schedule , they hold everything except the price constant and determine the quantities producers will offer for sale at all the possible prices. However, things other than price affect how much of a good or service people are willing to supply. These other determinants of supply are prices of resources, technology and productivity, expectations or producers, the number of producers, and the prices of related goods or services.