The document discusses the relationship between temperature, kinetic energy, and the thermal expansion and contraction of materials. It explains that when molecules are heated, they gain kinetic energy and move faster, causing them to spread farther apart and materials to expand in size. Conversely, when molecules cool down and lose kinetic energy, they move slower and get closer together, causing materials to contract. Examples provided include liquids expanding in a thermometer when heated and bridges being designed with expansion joints to accommodate changes in length due to varying temperatures.

1. * What is the
relationship between
temperature and
kinetic energy?
* Why do molecules
move faster when they
are heated?

2.  What happens when molecules get more energy?
What happens when molecules MOVE more?
Molecules move more
Molecules move moremore energy
Molecules spread out
more energy = expansion

3.  What happens when molecules get less energy?
What happens when molecules MOVE less?
Molecules move less
Molecules move lessless energy
Get close together
less energy = contraction

4. Warm-Up:
1.What happens to
pandesal if you leave it
on the table for an hour
after you take it out of
the oven? Why?
2. What is the best thing
to do to open a can
that is too difficult to
open after just taking it
out of the freezer?
(think about the molecules)

5.  THERMAL EXPANSION AND CONTRACTION

6. Video Questions:
What happens to molecules when
they are heated?
What makes molecules move?
What happens when molecules move
apart?
They move.
Energy (HEAT) makes molecules move
The material expands.

7. Thermal Expansion
The particles that make up matter move
more when heat is added.
When they move more, they spread out.
When they spread out, the matter they
are part of expands.

8. Do molecules
expand (get
bigger)?
NO!!!!!!!!!!
Do molecules
contract (get
smaller)?
NO!!!!!!!!!!

9. On the video next slide,
identify the situations
where thermal expansion
can be applied

11. The liquid in a thermometer tube expands
when it is heated and contracts when it is
cooled.

12. Thermal Expansion
Sidewalks that are built with thermal
expansion in mind don’t crack as much.

13. Thermal Expansion
Bridges are built with ‘joints’ so they don’t
crack when the temperature changes.

14. Space is left between railway tracks as an
allowance

15.  Space is left between railway tracks as an allowance for their expansion when
temperature increases, otherwise the rails may buckle. Similarly, long steel
bridges are designed to include expansion joints to allow for their expansion, by
fixing one end and resting the other end on rollers.

16. Why do objects expand when they are
heated?
Why do objects contract when they cool down?
Heat is energy.
More energy makes molecules move more.
When molecules move, they spread out,
which makes the object expand.
When objects cool down, they lose energy,
which makes molecules slow down.
When molecules move less, they get close
together, which makes the object contract.

17. PRACTICE QUESTIONS
You must explain what is
happening to the
MOLECULES in every
question.

18. 1. What would happen to any object if the
temperature changes from 20ºC to 80ºC? (Will it
expand or contract and WHY?)
2. What would happen to any object if the
temperature changes from 80ºF to 15ºF? (Will it
expand or contract and WHY?)
The object will expand because the molecules are
getting hotter (more energy) and will move faster
and farther apart.
The object will contract because the molecules are
getting colder (less energy) and will move slower
and closer together.

19. 3. When heated, the liquid in my water bottle
bulges out on the sides. Explain why the liquid
expands (think about what has happened to the
molecules)
4. A jar has been sitting in the refrigerator all
day. When I take it out, why is the jar difficult
to open?
The water expanded because the molecules got
hotter (more energy) and moved faster and farther
apart.
The jar contracted because the molecules got cold in
the refrigerator got closer together.

20. 20
A iron disc with a hole in it is heated.
Will the diameter of the hole (a) increase,
(b) decrease or (c) not change?
Q

21. 21
A nut is very tight on a screw. Which
of the following is most likely to free
it?
(a) Cooling the nut
(b) Heating the nut
(c) Heating the screw
(d) None of these

22. Summary
Thermal Expansion and
Contraction:
The molecules do not change
shape or size. They do not
contract or expand. Only the
object expands or contracts.
Why?: