Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Conceptual Question 9.9
Gas Bag
Posted by witch532
http://www.youtube.com/watch?v=wRFZXy-999I
Students were asked the following clicker questions (Classroom Performance System, einstruction.com) at the start of their learning cycle:
An unopened bag of potato chips is purchased at sea level, and then is brought up on a car trip into the mountains. As a result, the bag "inflates" and becomes rigid. This is because of a(n):
(A) increase in pressure inside the bag.
(B) decrease in pressure outside the bag.
(C) (Both of the above choices.)
(D) (I'm lost, and don't know how to answer this.)
Sections 30880, 30881
(A) : 5 students
(B) : 22 students
(C) : 5 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) : 0 students
(B) : 31 students
(C) : 3 students
(D) : 0 students
Correct answer: (B)
The principal cause of the bag "inflating" is the decrease in pressure in the air surrounding the bag as it is brought to a higher elevation. The pressure inside the bag then is greater than the ambient pressure outside. The absolute pressure inside the bag could increase due to an increase in temperature (using the ideal gas law), which is what some students discussed in choosing (C).
Pre- to post- peer-interaction gains:
pre-interaction correct = 69%
post-interaction correct = 91%
Hake, or normalized gain <g> = 72%
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