what is flow concept

 Flow Variables. A flow is a quantity which is measured with reference to a period of time. Thus flows are defined with reference to a specific period (length of time), e.g., hours, days, weeks, months or years. It has time dimension. National income is a flow. It describes and measures flow of goods and services which become available to a country during a year. Similarly all other economic variables which have time dimension, i.e., whose magnitude can be measured over a period of time are called flow variables. For instance, income of a person is a flow which is earned during a week or a month or any other period. Likewise investment (i.e., addition to the stock of capital) is a flow as it pertains to a period of time. Other examples of flows are : expenditure, savings, depreciation, interest, exports, imports, change in inventories (not mere inventories), change in money supply, lending, borrowing, rent, profit, etc. because magnitude (size) of all these are measured over a period of time.