A.3.5—Rates from linear graphs

A rate is change in the measured quantity per unit time or another independent variable. On a graph, the gradient is rise divided by run, with units that reveal the rate.

Use two points on the relevant line or curve, keep the time interval explicit and avoid mixing a secant average with an instantaneous rate.

If oxygen increases from 12 to 20 cm³ over 4 min, the average rate is 2 cm³ min⁻¹; a tangent at one moment may give a different instantaneous rate.

A steeper graph means a larger rate only when both axes and scales are comparable.