A small part of something may be special in some way and not give an accurate picture of the whole. How much a portion of something can help to estimate what the whole is like depends on how the portion is chosen. There is a danger of choosing only the data that show what is expected by the person doing the choosing. One way to make sense of something is to think how it is like something more familiar. Reasoning can be distorted by strong feelings.
Students begin an investigation of variables by examining the behavior of a pendulum.
Then students conduct multiple experiments to determine how many swings a pendulum system makes. The pendulum systems are of varying lengths. When the experiments are finished, the teacher demonstrates to the students how to use a number line to report the results of their experiments. The teacher then asks one team member to hang their pendulum system on the hook under the number representing the number of times the swinger made a round trip in 15 seconds. The teacher continues to select students to bring their pendulum systems to hang on the number line.