Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 4.53
Students were asked the following clicker questions (Classroom Performance System, einstruction.com) in the middle of their learning cycle:
A book rests on the surface of a (horizontal) table.__________ tells you that these two forces are equal in magnitude and opposite in direction:
The force of the Earth pulling on the book.(A) Newton's first law.
The force of the table pushing on the book.
(B) Newton's second law.
(C) Newton's third law.
(D) (I'm lost, and don't know how to answer this.)
Sections 30880, 30881
(A) : 16 students
(B) : 2 students
(C) : 17 students
(D) : 4 students
This question was asked again after displaying the tallied results with the lack of consensus, in order to see if students were going to be able to discuss and determine the correct answer among themselves, with the following results. Note that in contrast to the usual practice of no comment, the instructor answered many clarification questions from the students ("Is the force of the Earth pulling on the book the weight force?" "Is the book also pushing on the table?").
Sections 30880, 30881
(A) : 28 students
(B) : 1 student
(C) : 5 students
(D) : 1 student
Correct answer: (A)
The upwards normal force of the table on the book must be equal in magnitude to the downwards weight force of the Earth on the book, due to Newton's first law, as these forces exerted on the stationary book must sum to zero. These two forces cannot be a Newton's third law pair (an "interaction pair") because they fail the last two parts of the three-part "POF-OST-ITO" checklist ("Pair of Opposite Forces; Of Same Type; Involving Two Objects," Benjamin Crowell, Fullteron College, CA) fails.
Pre- to post- peer-interaction gains:
pre-interaction correct = 41%
post-interaction correct = 80%
Hake, or normalized gain <g> = 66%
[Follow-up question.]
__________ tells you that these two forces are equal in magnitude and opposite in direction:
The force of the book pushing on the table.(A) Newton's first law.
The force of the table pushing on the book.
(B) Newton's second law.
(C) Newton's third law.
(D) (I'm lost, and don't know how to answer this.)
Sections 30880, 30881
(A) : 8 students
(B) : 2 students
(C) : 29 students
(D) : 0 students
This question was asked again after displaying the tallied results with the lack of consensus, with the following results. No comments were made by the instructor, in order to see if students were going to be able to discuss and determine the correct answer among themselves.
Sections 30880, 30881
(A) : 7 students
(B) : 0 students
(C) : 27 students
(D) : 0 students
Correct answer: (C)
The upwards normal force of the table on the book must be equal in magnitude to the downwards normal force of the book on the table, due to Newton's third law, as these forces satisfy all three parts of the "POF-OST-ITO" checklist ("Pair of Opposite Forces; Of Same Type; Involving Two Objects").
Pre- to post- peer-interaction gains:
pre-interaction correct = 74%
post-interaction correct = 79%
Hake, or normalized gain <g> = 20%
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