Section 2: Measurement: Errors, Accuracy, and Precision

Section 2: Measurement: Errors,
Accuracy, and Precision
Lesson 1
o Remind the students to begin a new page in their Active Physics Log. The
heading of the page should be Section 2: Measurement. Also record the
section and page number in your Table of Contents
What do you see?
o Notice that there are four people in the cartoon. Ask your students if any
of the four are involved in taking measurements? What measuring tool(s)
are they using? And what are they measuring?
o Write your answer in your log.
o (4 minutes)
What do you think?
o Read both statements regarding measurements to your students and ask
them to decide whether they can decide whether anyone made a mistake in
measuring. Tell them to record their answers in their log.
o (4 minutes)
o The class will make measurements in order to determine which are
accurate and/or precise.
o The class must decide on an agreed upon distance, i.e. the length of the
hall, the perimeter of the classroom, ……
o One member of the lab team will walk this distance and count the number
of strides.
o Remind the class to record all their data in their journal/log.
o Using a meter stick, the team must measure the length of a single stride.
o Multiply the length of a stride by the number of strides to get the distance
of the agreed upon distance.
o Every lab team must write the determined distance on the board.
o The students must answer the following questions (found on page 23) in
their journal/log.
 1-Do all the measurements agree? By how much do they vary?
 2-Why do you think there are differences among the measurements
made by different groups? List as many reasons as you can.
 3-Suggest a way of improving your measurements.
o Now measure the agreed upon distance with a single meter stick, by
moving it over and over. Record this distance in your log and record it on
the board. Also, answer all of the following questions in your log.
 The students must answer questions 1, 2, & 3 from above
regarding this different method of measuring.
Ask the class what would have happened if they had used a tape
measure instead.
 Ask the class, is there a method that would produce a result in
which everyone would get exactly the same value?
o (20 minutes)
Systematic vs Random Errors
o Discuss the differences between the following terms – systematic error
and random error. Mention that no measurement is perfect, that there is
always a random error in every measurement.
o Now have the class decide whether there were any systematic errors when
earlier measuring the distance. Also estimate the size of the random error
in both of the techniques used in measuring the distance.
o (8 minutes)
Reasonable Estimates
o On page 24 there are 9 examples of estimates. Read each one aloud and
have the class vote individually if it is a reasonable estimate. An
excellent technique of getting the entire class to respond is to ask each
student to hold their thumb up (yes) or down (no). This lets you know that
they are involved in the activity and whether they understand the concept.
It is called Checking For Understanding and I will include the expression
CFU in most every lesson to remind you to make sure that you constantly
ask your students to respond.
o (5 minutes)
Homework at the end of Lesson 1
o Physics to Go p.32
 #1, 3, 4
o Read Physics Talk and draw the diagrams at top of page 27 in your log
being sure to label them as accurate and precise, precise not accurate and
accurate but not precise. Draw a fourth diagram that would illustrate
neither accurate nor precise.