Physics clicker question: what is not a vector?

Physics 5A, Fall Semester 2007
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Chapter 2.2

Students were asked the following clicker question (Classroom Performance System, einstruction.com) near the beginning of their learning cycle:

[0.3 participation points.] Consider the following list of quantities:
Position.
Displacement.
Distance traveled by an object.

How many of the above quantities are vectors? _____.

Correct answer: 2.

Student responses
Sections 0906, 0907
"1" : 16 students
"2" : 28 students
"3" : 2 students

Teachable moment! Students were then asked to identify the one quantity that was not a vector, eliciting various responses, most notably "position." Following discussion ensues:

• "Displacement" is a vector, pointing from the initial to the final location.
  
• "Distance traveled by an object" is not a vector but a scalar, and in one-dimensional travel may move back and forth along itself.
  
• "Position" is a vector, as it points from the origin to the location. Many students were thinking of a location as just a point, and thus not a vector. Or a few students had considered a special case that if an object starts from the origin, then its initial position is then a point and not a vector; but this brings up the special case of a null vector.