Responses to Temperature
Change
Thermal Expansion (solids/liquids)
Kinetic Theory (gases)
Lesson 11
Lesson 11: Thermal Expansion & Kinetic Theory of Gases
AP Physics B Objectives
II.B.2. Heat transfer and thermal expansion
Students should understand heat transfer and thermal expansion,
so they can:
a) Calculate how the flow of heat through a slab of material is affected by
changes in the thickness or area of the slab, or the temperature difference
between the two faces of the slab.
b) Analyze what happens to the size and shape of an object when it is
heated.
II.C.1. Ideal Gases
a) Students should understand the kinetic theory model of an ideal gas, so
they can:
(4) Explain qualitatively how the model explains the pressure of a gas in terms of
collisions with the container walls, and explain how the model predicts that, for fixed
volume, pressure must be proportional to temperature.
Lesson 11: Thermal Expansion and Kinetic Theory of Gases
Student Objectives
 Students will be able to
1.
2.
Determine the thermal expansion of a material.
Explain the kinetic theory of gases.
Thermal Expansion
 When the temperature of a substance rises, its
molecules move at higher speeds. Collisions
with neighboring molecules are more energetic.
Molecules use more space to move around.
 This causes most substances to expand when
their temperature goes up. Mathematically:
 L = LoT
 L is change in length
  is coefficient of linear expansion
 Lo is original length of substance
 T is change in temperature
 Sample problem: If the Eiffel tower is 301 m tall on a day
when the temperature is 22o C, how much does it shrink
when the temperature drops to 0O C? The coefficient of
linear expansion is 12 x 10-6 K-1 for the iron the tower is
made from.
What about when you raise the
temperature of a gas?
The kinetic energy increases with
temperature, but because a gas is
compressible, predicting how it will expand
is more complicated than for a solid or a
liquid.
Gases are compressible and require a different
approach – the Kinetic Theory of Gases
1. Gases consist of a large number of molecules
that make elastic collisions with each other and
the walls of the container.
2. Molecules are separated, on average, by large
distances and exert no forces on each other
except when they collide.
3. There is no preferred position for a molecule in
the container, and no preferred direction for the
velocity.