CHAPTER 4
Applying Ideas
ACTIVITY 4: Explanations Involving Gases
Comparing the Class Consensus and Scientists' Ideas
During the activities in this chapter, the class developed ideas about how
microscopic properties of materials (like the average speed or average KE of
particles) affected macroscopic properties (like pressure and temperature).
Most importantly, you explored ideas about the SPT mechanisms for both
pressure and temperature, which allowed you to use the microscopic
properties of particles to explain phenomena at the macroscopic level.
Your instructor will give you a copy of the handout Scientists’ Ideas:
Interactions and Gases. Take a few minutes to review the Scientists’ Ideas and
make sure they correspond to the ideas the class has developed. In the space
below each of the scientists’ ideas you should make a note of any evidence (or
examples) you have seen in this chapter that supports the idea.
In this activity, you will work through some additional explanations of realworld events or phenomena in terms of ideas that we developed in class. As a
summary, here are the three big ideas that you should draw on when
explaining phenomena involving gases.
Big Idea
Conservation of Energy
SPT mechanism for temperature
SPT mechanism for pressure
© 2008 PSET
Use this idea…
When you need to justify or decide how
temperature changes, if at all. Usually
draw a Micro I/O energy diagram.
When you need to make connections
between temperature, average KE and
average speed. Usually draw a Micro
I/O energy diagram and construct a
Macro/Micro table.
When you need to justify or decide how
the pressure changes when other
macroscopic properties change. Usually
construct a Macro/Micro table.
4-85
Chapter 4
Sometimes you need to use two or more of these big ideas to explain the
phenomena. In those cases it may be convenient to break up the explanation into
parts, drawing a diagram and writing a narrative associated with each big idea.
Explanation #1: As you drive long distances at a high speed, the tires on your
car usually get warmer and the air pressure increases. Explain both why the
tires get warmer and why the air pressure increases.
(a) Draw a micro I/O energy diagram describing what happens to the particles of
rubber in the tires. (Although rubber is a solid, in this case the description of what
happens to its particles is the same as if the rubber was a gas.) Assume the initial
temperature of the rubber particles is 200C.
(b) Explain why the tire gets warmer
4-86
Activity 4: Explanations Involving Gases
(c) Now consider the air in the tires. Fill in the Macro/Micro Table (to show what
happens to the air pressure in the tire):
Temp.
Mass
Volume
Avg.
Avg.
Total #
# collisions/sec
Oomph/
KE
Speed
particles
/area
collision
Pressure
(d) Explain why the air pressure increases in the tires
4-87
Chapter 4
Explanation #2: When inflating a completely flat tire, at first the pressure
inside the tire remains constant as air is added. Then, after it can no longer
expand, adding more air causes its pressure to increase. (Ignore the slight
increase in temperature of the tire.) Explain each effect.
(a) First consider why the air pressure remains constant as air is added and the
volume increases. Fill in the Macro/Micro Table:
Temp.
Mass
Volume
Avg.
Avg.
Total #
# collisions/sec
Oomph/
KE
Speed
particles
/area
collision
Pressure
(b) Explain why the air pressure remains constant as air is added and the volume
increases.
4-88
Activity 4: Explanations Involving Gases
(c) Next consider why the pressure increases as air is added and the volume remains
constant. Fill in the Macro/Micro Table:
Temp.
Mass
Volume
Avg.
Avg.
Total #
# collisions/sec
Oomph/
KE
Speed
particles
/area
collision
Pressure
(d) Explain why the pressure increases as air is added and the volume remains
constant.
Participate in a class discussion to review the Explanations.
4-89