On This Page
Overview
Experimental error and uncertainty are essential parts of physics. They describe the difference between measured values and ideal or accepted values, as well as the limits on how precisely a result can be known.
In science, uncertainty does not mean ignorance or failure. It means the result is reported with an honest recognition of measurement limits, instrument limits, procedure limits, and natural variation.
Error and Uncertainty
Error often refers to the difference between a measured value and a true or accepted value. Uncertainty refers to the range within which the true value is reasonably expected to lie based on the measurement process.
The word error does not always mean a mistake. Some error is unavoidable because instruments and observations are limited.
Random Error
Random error causes measurements to vary unpredictably from trial to trial. It may come from small changes in reaction time, environmental conditions, reading instruments, or natural fluctuations in the system.
Repeating measurements and averaging results can reduce the effect of random error, although it does not remove all uncertainty.
Systematic Error
Systematic error shifts measurements consistently in one direction. It may come from a miscalibrated instrument, a flawed procedure, a zero offset, or an assumption that does not match the experiment.
Averaging repeated trials does not usually remove systematic error. The procedure, instrument, or model must be corrected.
Reporting Results
A responsible experimental result includes a value, a unit, and an indication of uncertainty when appropriate. The number of significant figures should match the precision of the measurement.
Graphs, data tables, repeated trials, percent error, uncertainty ranges, and written explanations can all help communicate the quality of the evidence.
Importance in Physics
Uncertainty helps scientists judge whether a result is meaningful. If two measurements differ by less than their uncertainty ranges, the difference may not be significant.
Understanding uncertainty also helps prevent overconfidence. A physics conclusion should be supported by evidence, but the strength of that support depends on the quality and limits of the measurements.