Practical definitions and formulas

• What is the rule for multiplying or dividing uncertainties

  Add the percentage uncertainty
• What is the rule for adding or subtracting uncertainties

  Add the absolute uncertainties
• How is absolute uncertainty measured for a data set

  Half of the range
• How is absolute uncertainty calculated for singular readings

  Uncertainty is the smallest reading it goes to

  Eg mass = 5.41 kg

  So uncertainty is +-0.01 kg
• Percentage uncertainty calculated

  Absolute uncertainty / mean value x100

  For a singular value divide by the value
• Fractional uncertainty calculated

  Absolute uncertainty/ mean value
• Precision

  How consistent the results are
• Accuracy


  How close you are to the true value
• Random error

  Unpredictable error

  Take multiple measurements to find the mean.
• Systematic error

  Affects all measurement by the same amount

  Eg a zero error

  Does not affect the gradient
• Measurement error

  Difference between a measured value and the true value
• Resolution

  Smallest change in a measuring instrument which gives a perceptible change
• Independent variables

  Variable tha is changed
• Dependant variable 


  Variable you measure
• Control variables

  Variables kept constant as they may affect the outcome of the investigation
• What is an error bar

  Represents the range of an uncertainty on the graph
• Percentage uncertainty in a graph

  Line of best fit - line of worst fit/ line of best fit x100

  LOBF - LOWF /LOBF x100