Random error
Unpredictable, non-directional variations in measurements caused by uncontrollable factors such as environmental fluctuations, observer judgment, or inherent instrumental sensitivity. Random errors can be minimised by repeated measurements and averaged. Unlike systematic errors, they cancel out statistically over multiple trials.
Real World
When students time a pendulum with a stopwatch, slight variations in human reaction time cause each reading to differ by a few hundredths of a second — averaging 20 swings reduces this random scatter significantly.
Exam Focus
State that random errors are reduced by repeating and averaging — never say they are 'eliminated', as mark schemes distinguish the two.
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