Which pair is cited as an example of flow vs quantity relationships?

• A. Pounds per linear foot on a beam
• B. Pounds per square foot on a floor
• C. Power vs electricity
• D. Peak heating load vs annual heating

Answer: (D)

Flow vs quantity is about comparing a rate to a total over time. Peak heating load represents the maximum rate at which heat is needed (a flow, energy per hour), while annual heating is the total amount of energy used over a year (a quantity). This pair directly contrasts a rate with its accumulated total, which is the essence of flow versus quantity. The other options don’t capture that time-based contrast as clearly: pounds per linear foot or per square foot are load densities distributed along a dimension (rates per length or area), not a time-based flow versus total; and power versus electricity mixes a rate with a resource in a way that doesn’t illustrate the flow-vs-quantity relationship as cleanly.