a movement on the demand curve will take place when there is
Demand curve There is movement along a demand curve when a change in price causes the quantity demanded to change.[5] It is important to distinguish between movement along a demand curve, and a shift in a demand curve. Movements along a demand curve happen only when the price of the good changes.[6] When a non-price determinant of demand changes the curve shifts. These "other variables" are part of the demand function. They are "merely lumped into intercept term of a simple linear demand function." [6] Thus a change in a non-price determinant of demand is reflected in a change in the x-intercept causing the curve to shift along the x axis.[7]
IS–LM model Given expectations about returns on fixed investment, every level of the real interest rate (i) will generate a certain level of planned fixed investment and other interest-sensitive spending: lower interest rates encourage higher fixed investment and the like. Income is at the equilibrium level for a given interest rate when the saving that consumers and other economic participants choose to do out of this income equals investment (or, equivalently, when "leakages" from the circular flow equal "injections"). The multiplier effect of an increase in fixed investment resulting from a lower interest rate raises real GDP. This explains the downward slope of the IS curve. In summary, this line represents the causation from falling interest rates to rising planned fixed investment (etc.) to rising national income and output.