Using Scientific
Measurements
Uncertainty in Measurements
All measurements have uncertainty.
1. Measurements involve estimation by
the person making the measurement.
2. Measuring devices are limited in their
precision
Accuracy and Precision
Accuracy – the
closeness of
measured values to
the true or accepted
value
Precision – the
closeness of
repeated
measurements of
the same quantity
Percent Error
• Used to compare measured values to the
true or accepted value.
 Measured Value  Accepted value 

 x100%
accepted value


Percent Error
Sample Problems
1. Calculate the percent error in a length
measurement of 4.25 cm if the correct value is
4.08 cm.
2. The actual density of a certain material is 7.44
g/cm3. A student measures the density of the
same material as 7.30 g/cm3. What is the
percent error of the measurement
Counting Significant Figures
Determine the number of significant figures in each
of the following numbers:
0.003042
50.0
1.4030
10.47020
1000
250.
1000.
65,321
1000.00
2.00 x 102
0.060
1.004 x 105
Rounding to Significant Figures
Round each of the following numbers to three
significant digits:
1,566,311
2.651 x 10-3
84,592
0.0011672
0.07759
Calculations with significant figures
1. Find the volume of a cube that is 3.23 cm on
each edge.
2. What is the sum of 67.14 kg and 8.2 kg?
3. Calculate the density of a 17.982 g object that
occupies 4.13 cm3.