A student investigates how the concentration of a surfactant additive affects the relative wear rate of a steel alloy bearing. The graph shows the results of this investigation.
A relative wear rate of 1.0 represents the wear rate with zero additive (the baseline). A value of less than 1.0 indicates a reduced wear rate (better lubrication), while a value greater than 1.0 indicates an increased wear rate.
Adding any amount of surfactant additive increases the wear rate of the bearing.
A surfactant concentration above 60 mmol dm−360\text{ mmol dm}^{-3}60 mmol dm−3 decreases the relative wear rate of the bearing.
Using a surfactant concentration of exactly 60 mmol dm−360\text{ mmol dm}^{-3}60 mmol dm−3 does not increase or decrease the wear rate compared to using no additive.
Changing the surfactant concentration has no significant effect on the relative wear rate of the bearing.