This dialog explores the concept of distance. Most students know how to measure distance in some situations. We raise many issues about measurement, drawing on the student's background to illustrate these issues in partially familiar situations.
The module starts with the student asked to measure some distances on the screen. A ruler is displayed, larger than the separation between points.
Several results are drawn from this initial measurement operation. First, the student becomes conscious of the process involved in the measurement operation, the ingredients of an operational definition. Second, the student discovers that not everybody makes the same measurement in a given situation. This idea receives considerable attention in the remainder of the unit. Thus, while students started out to measure ``the distance,'' each person seems to have his or her own individual distance, the result of the individual measurement! This common feature of scientific measurements leads to discussion of average and standard deviation and sheds important light on the measurement process, all in a context familiar to the students.
In the next distance measurement, the positions are further apart then the length of the ruler. So a new set of ``directions'' are needed. Several other operational definitions of distance are also introduced and used by the student. Thus the student measures distance across a canyon with sound echos.
Another point raised by the unit is that of different ways of measuring ``something'' that, in each case, is called distance. The issue is raised as to why each of these different processes can be said to measure the ``same thing.''