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 PrecisionAccuracy – 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.

%100xvalueaccepted

valueAcceptedValueMeasured

Percent ErrorSample 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 FiguresDetermine the number of significant figures in each

of the following numbers:

0.003042

1.4030

1000

1000.

1000.00

0.060

50.0

10.47020

250.

65,321

2.00 x 102

1.004 x 105

Rounding to Significant FiguresRound 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.