Measurements, Accuracy and
Errors
UNIT 1 - INTRODUCTION TO PHYSICS
Vocabulary
Measurement
magnitude
quantitative
Qualitative
precision
accuracy
Parallax
significant figures
scientific notation
Length
volume
area
Constants
electromagnetic spectrum
Meniscus
beaker
graduated cylinder
Thermometer
triple beam balance
meter stick
Measurements, Accuracy and Errors
 Physics is a quantitative science.
 Physicists deal in numbers.
 Physicist's numbers are often measurements, not
the pure numbers of the mathematician.
 Therefore, physicists measure things.
Measurements, Accuracy and Errors
 As a physicist, you have to deal with four different types
of numbers:
 Pure
"theoretical" numbers – numbers in
formulas.
 Counts - a measurement that does not need a
measuring instrument. It is always a whole
number.
 Measurements - mass, length, volume, etc.
 Calculated values – values calculated from
formulas.
Measurements, Accuracy and Errors
Precision versus Accuracy
Precision is the state or quality of being exact.
It is the ability of a measurement to be consistently
reproduced.
Precision is only as good as the tools used to measure.
To be precise, record exactly what you measured.
Measurements, Accuracy and Errors
Accuracy refers to how close or far a determined
experimental value may be from the actual value.
Accuracy refers to the correctness of a single
measurement.
Accuracy is determined by comparing the
measurement against the true or accepted value.
Measurements, Accuracy and Errors
Measurement, Accuracy and Errors
 All experimental measurements are subject to some
errors, other than those caused by carelessness.
 Common errors which occur are parallax errors, zero
errors and reading errors.
 Parallax errors are errors which occur when the eye
is not placed directly opposite a scale when a reading
is taken.
Insert parallax error diagram
Measurements, Accuracy and Errors
 Zero errors occur when a measuring instrument does
not indicate zero when it should.
 Instruments should be adjusted to read “zero” before
measuring is done.
 Reading errors occur when the reading lies between
the scale divisions and one has to guess the value.
Insert Reading error diagram
Measurements, Accuracy and Errors
 Significant Figures and Rounding
 The number of significant figures in a value is the
number of figures in that value ignoring leading or
trailing zeros and disregarding the position of the
decimal point.
 Significant Figures give an indication of the accuracy
of a reading.
Insert Significant Figures diagram
Measurements, Accuracy and Errors
 Rounding is the process of reducing the number of
figures quoted.
 The last significant figure is dropped and the new
last figure changed depending on the one dropped.
Refer to significant figures diagram
Measurements, Accuracy and Errors
 Exponential Notation and Scientific Notation
 For large numbers like 283,000 it is impossible to
say how many of the figures are significant because
the zeros have to be included to show the magnitude.
 In this case we can use exponential notation and
scientific notation to represent the value in the
correct amount of significant figures.
2.82 x 105
Measurements, Accuracy and Errors
 Very large or very small numbers take a long time to
write out and are difficult to read.
 Writing measurements using scientific notation
helps keep our values accurate, readable and small.
Insert Order of Magnitude