what can affect the demand for a product
Price of Related Goods: Demand for the given commodity is also affected by change in prices of the related goods. Related goods are of two types: (i) Substitute Goods: Substitute goods are those goods which can be used in place of one another for satisfaction of a particular want, like tea and coffee.
In drawing the demand schedule or the demand curve for a good we take income of the people as given and constant. When as a result of the rise in the income of the people, the demand increases, the whole of the demand curve shifts upward and vice versa. The greater income means the greater purchasing power.