In this article, we will present the HEC BB bag, a simple but elegant model originally invented to help students imagine how air molecules move around in vacuum. The HEC BB bag is made by packing 20 to 30 BBs in a resealable plastic bag of several tens of square centimeters (see Fig. 1). When inflated fully via a straw, the volume of the bag is about 5 L in volume (see below for specifications).

1.
K.
Itakura
,
Hypothesis–Experiment Class
(Kasetsu) (original: Kisetsusya, 1969, translated:
Kyoto University Publishing
, edited by Haruhiko Funahashi,
2019
).
3.
For example,
A.
Nakamura
,
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(
Kindle e-Book
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2022
) and
M.
Ito
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(
Kasetu-sha Co. Ltd
.,
Tokyo
,
1998
).
4.
Y.
Takeda
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Related materials for ‘Tigers die and leave skin’, the story of the development of molecular motion models
,”
Wakaba Shobō
(
1991
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5.
P. G.
Hewitt
,
Conceptual Physics
, 10th ed. (
Pearson Addison-Wesley
,
San Francisco
,
2006
).
7.
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,
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(
National Academies Press
,
Washington, DC
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8.
R. G.
Tobin
 et al, “
Where does energy go when it’s ‘gone’? Promoting understanding of energy dissipation
,”
Am. J. Phys.
87
,
569
576
(
2019
).
9.
Note that, generally, the effect of air friction is small compared to the effect of friction at the pendulum support (fulcrum). Energy dissipation at the support happens due to the interaction between the atoms at the fulcrum (string of the pendulum and atoms of the support), which results in the acceleration of these atoms (warming). This warming could also be modeled by shaking the BB bag and showing that the BBs are speeding up.
10.
C. W. J. M.
Klaassen
,
H. M. C.
Eijkelhof
, and
P. L.
Lijnse
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Considering an alternative approach to teaching radioactivity
” in
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(
1990
), pp.
304
316
.
11.
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and
M.
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Student understanding of emergent aspects of radioactivity
,”
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,”
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14.
Although a similar strategy is used by the Classbook “Springs and Force” that precedes Camp and Clement’s instruction, we reference the strategy from Camp and Clement’s curriculum as it is freely available in English. Interested readers are encouraged also to read “
Hypothesis–Experiment Class: Put into Practice with ‘Springs and Force’
” (
Kasetu-sha Co., Ltd
.,
Tokyo
,
1979
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15.
S.
Novick
and
J.
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,
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(
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Johnson
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Die Teilchenstruktur der Materie im Physik- und Chemieunterricht,
edited by
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Berlin
,
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144
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A. K.
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and
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18.
A. G.
Harrison
and
D. F.
Treagust
, “
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,”
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29
,
45
85
(
2001
).
19.
In theory, a pump could be used to remove air from the container holding the BBs. In practice, however, this is only feasible if the walls of the container are stiff. Unfortunately, stiff walls prohibit the tactile experience of feeling the balls hit against your hand, representing pressure from a gas.
20.
G. J.
Wiener
,
S. M.
Schmeling
, and
M.
Hopf
, “
Introducing 12 year-olds to elementary particles
,”
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,
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(
2015
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21.
A. G.
Harrison
and
D. F.
Treagust
, “
Secondary students’ mental models of atoms and molecules. Implications for teaching chemistry
,”
Sci. Educ.
80
,
509
542
(
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).
22.
M.
Becker
and
M.
Hopf
, “
Der Energie-Feld-Ansatz: Design-Forschung zur Entwicklung und Evaluation eines Unterrichtskonzeptes für den Energieunterricht der Oberstufe
,”
PhyDid B-Didaktik der Physik-Beiträge zur Frühjahrstagung
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