1. Accuracy vs. Precision

2. Qualitative vs. Quantitative
Qualitative measurements give results in a descriptive nonnumeric form. (The results could be used to identify an unknown or to help describe one.)
*Examples: ___________, ___________, blue, __________...
Quantitative measurements give results in numeric form. (The results of a measurement contain a _____________.)
*Examples: 4’6”, __________, 22 meters, __________...
Accuracy vs. Precision
Accuracy is how close a ___________ measurement is to the ________ __________ of whatever is being measured.
Precision is how close ___________ measurements are to _________ ___________.
shiny
heavy
cold
number
600 lbs.
5 ºC
single
true
value
several
each
other

3. Accuracy vs. Precision

4. Practice Problem: Describe the shots for the targets.
Bad Accuracy & Bad Precision
Good Accuracy & Bad Precision
Bad Accuracy & Good Precision
Good Accuracy & Good Precision

5. Evaluating the Accuracy of a Measurement
The “Percent Error ” of a measurement is a way of representing the accuracy of the value. (Remember what accuracy tells us?)
% Error = (Accepted Value) − (Experimentally Measured Value) x (Accepted Value)
Practice Problem:
A student measures the density of a block of aluminum to be approximately 2.96 g/mL. The value found in our textbook tells us that the density was supposed to be 2.70 g/mL. What is the accuracy of the student’s measurement?
(Absolute Value)
% Error = |2.70−2.96| ÷ 2.70 =
…x 100 =
9.63% error