Affect as a verb means "to influence."
The temperature affects the growth rate of
the bacterial sample.
Affect as a noun has a specialized meaning in medicine and psychology, referring to moods and feeling as distinct from thoughts or knowledge.
Dua (1989) constructed the Thoughts and Real-Life
Experience Scale (THARL) to assess the degree of positive and
negative affect experienced by people as a result
of their thoughts and day-to-day interactions.
--J. K. Dua, "The Role of Negative Affect and Positive Affect in Stress, Depression, Self-Esteem, Assertiveness, Type A Behaviors, Psychological Health, and Physical Health," Genet Psychological Monographs
Effect as a verb means "to bring about, to produce," or to "accomplish something."
The temperature reversal effected a major
slowdown in the bacterial growth rate.
Effect as a noun means "result."
Increased bacterial growth rate was one major
effect of the rise in pond temperature.
Impact as a verb means "strike with a blow" or "to pack firmly together."
The wisdom tooth impacted the molar.
Impact as a noun means "a collision."
The constant impact of the two gear
mechanisms on each other eventually produced metal fatigue in
several sprockets.
Do not use impact as a verb in place of "to affect."
The temperature impacts the growth rate of
the bacterial sample.
The temperature affects the growth rate of
the bacterial sample.
Do not use impact as a noun in place of "effect."
The release of hydrocarbons has had a significant
impact on the depth of the ozone layer.
The release of hydrocarbons has had a significant
effect on the depth of the ozone layer.
