Category IV Physical Science Examples
Providing practice
Matter and Molecules
The unit provides a sufficient number and variety of practice tasks for most key
ideas. For example, consider the following concepts and key ideas:
a) Perpetual molecular motion: Molecules are perpetually in motion
b) Relation between temperature and molecular motion: Increased temperature
means greater molecular motion, so most materials expand when heated
c) Different arrangement and motion of molecules in solids, liquids and gases: In
solids, the [molecules] are closely locked in position and can only vibrate; In
liquids, the molecules are more loosely connected, and can slide past one
another; In gases, molecules are free of one another except during
occasional collisions
d) Evaporation: Some molecules may escape into a gas
From the very beginning, Matter and Molecules shows its commitment to giving
students opportunities to practice using knowledge (Science Book, pp. T-5 and
T-6). Matter and Molecules meets that commitment by giving students
opportunities throughout the unit to practice using ideas related to the kinetic
molecular theory to explain a variety of phenomena.
The material provides a sufficient number of tasks in a variety of contexts to
practice the idea “perpetual molecular motion.” For example, in the Activity Book
student are asked to use the ideas that molecules are constantly moving to
explain how perfume and other smells travel (pp. 14st), why a basketball does
not get flat when one sits on it (p. 17s), why a syringe plunger moves back out
when one lets it go (p. 20s), what will happen if the valve of a scuba tank full of
air is opened (p. 21st), what happens to the air as it is first pumped into a bicycle
tire and later released (p. 22st), and how sugar dissolves in water (p. 27s).
The material provides a sufficient number of tasks in a variety of contexts to
practice the relation between temperature and molecular motion. For example,
students use the idea that increased temperature means increased molecular
motion to explain why sidewalk expansion joints are wider in winter than in the
summer, why heating loosens a jar lid, why the column of the colored liquid in a
thermometer rises when the thermometer is placed into warm water, why a dime
placed on the wetted rime of a bottle “jumps” when we wrap our hands around
the bottle, and why a balloon placed on a large cold bottle inflates if we wrap our
hands around the bottle. In addition, students use the idea that increased
temperature means increased motion along with other ideas (such as the forces
between molecules in solids, liquids, and gases) to explain phenomena of
melting, solidifying, evaporation, and condensation of different substances.
The material provides a few tasks to practice the different arrangement and
motion of molecules in solids, liquids and gases. Students are asked to pick a
substance and draw its molecules in the three states of the substance (p. 10s).
Students use the ideas of the different molecular arrangement and motion in the
three states (along with other ideas) to describe and explain phenomena related
to the changes of state (e.g., pp. 39st, 40st, 42-43st, 45s, 46s, 47-48st).
However, only once are students asked to use the idea of molecular
arrangement and motion in the three states to explain differences in macroscopic
properties of solids, liquids, and gases (p. 10s). (Students are asked to explain
why we can compress air but not water in a syringe in lesson cluster 4.)
The material provides a sufficient number of tasks in a variety of contexts to
practice evaporation. For example, after the student text explains evaporation of
water in general, students are asked to give examples in which water evaporates
and explain evaporation in one of these examples. In addition, students are
asked to explain what is happening to the water at the surface of the ocean,
evaporation of alcohol, and why “fog burns off.”
For all four ideas, Matter and Molecules includes novel tasks in the sense that
students are asked to explain phenomena not previously explained in the student
text. For example, after reading a molecular explanation of the thermal expansion
of a metal ball, students are asked to explain the expansion of a jar lid and of
expansion joints in sidewalks. After reading a general explanation of thermal
expansion of gases, students are asked to explain a) what happens when one
places a dime on an empty soda bottle from the refrigerator and then warms the
bottle up, and b) what happens when one places a balloon over the rim of an
empty soda bottle from the refrigerator and then warms the bottle up.
Matter and Molecules provides a sequence of questions or tasks for which the
complexity is progressively increased. For example, in lesson cluster 6, students
are asked to use the idea “increased temperature means increased molecular
motion” to explain the simpler phenomena of thermal expansion. In clusters 7-9,
students are asked to integrate this idea together with the different arrangement
and motion of molecules in the three states and the idea of forces between
molecules, to explain the more complex phenomena of changes of state.
Matter and Molecules provides feedback that is gradually reduced. Practice tasks
early in the unit ask students to state what the two questions are that a good
explanation must answer, and then, for each explanation they are asked to give,
the unit reminds them “Make sure you answer both questions.” (Question set 4.4,
p. 23-24s) In the next cluster, students are given a bit less guidance – e.g., in
question set 5.3 students are reminded “use the parts of an explanation that you
have learned about.” (p. 29s) In the review to category 6, students are told to
“talk about substances and molecules in each answer.” (p. 38s) In clusters 7-9,
reminders are rarely given.