A Classmate Is Having Difficulty Understanding Two Sets of Accounting

Essay

A classmate is having difficulty understanding two sets of accounting terms, variable and fixed costs, as opposed to period and product costs. He understands that variable costs change during an accounting period while fixed costs do not. However, he explains that a period cost implies that it is for a period of time and is, therefore, also fixed. Does his assumption imply that all product costs are then variable?
Required: Assist your classmate in being able to distinguish between these terms.