Which equation is commonly used to relate flow, area, and velocity?

• A. Q = v × A
• B. Q = A ÷ v
• C. Q = A × v
• D. Q = A − v

Answer: (C)

Flow rate is found by multiplying how fast the fluid is moving by the cross-sectional area through which it passes. This product gives the volumetric flow rate, with units of volume per time (for example, m^3/s) when velocity is in m/s and area is in m^2. So the equation is Q = A × v. The form is the same as v × A due to multiplication being commutative, so it represents the same relationship. The other forms don’t yield the correct flow rate: dividing area by velocity would not produce a flow rate and would have mismatched units, and subtracting velocity from area mixes incompatible units.