This presentation is based from the book of FOCUS SCIENCE..

2. •Heat flows from warmer objects to cooler objects. When
a warmer object is in contact with a cooler object, it will
transfer heat to the cooler object.
•This will go on until both objects have the same
temperature. At this point, they are in the state of
thermal equilibrium.
•For example, a bottle of soda is taken out from
refrigerator and placed on a table. The table which is at
room temperature, will transfer heat to the bottle.
Eventually, their temperature will be equal and thermal
equilibrium will be achieved.

3. •Most matter expands when heated and contracts
when cooled.
•Two common examples of the effects of heat are
a boiled egg and a thick glass cracking when hot
water is poured onto them.
•The increase in size of objects when they are hot
is called expansion. The decrease in their size
when they are cooled is called contraction.

4. •The atoms or molecules in a solid vibrate at all
temperatures.
•As the temperature increases, they vibrate more
vigorously and this pushes the atoms further
apart. The volume of the solid increases and the
expansion is said to occur.

5. cold hot
Arrangement of particles in a solid
•When the solid is cooled, the atoms vibrate more
slowly and they become closer together. The volume
of the solid decreases and contraction occurs.

6. •When a liquid is heated, the molecules of the liquid
have more energy and move more vigorously. The
movement of the molecules gradually overcomes the
forces of attraction between molecules, allowing them
to have greater freedom to move over greater
volumes. Thus, the liquid expands.
cold hot
Arrangement of particles in a liquid

7. •At a lower temperature, the molecules of the
liquid have less energy and move closer to each
other. This causes the volume of the liquid to
decreases and the liquid contrasts.

8. •The molecules of a gas are far part compared with the
molecules in a solid and a liquid. The gas molecules
move at a high speeds in all direction.
•If a gas is confined in a container whose volume is
variable, the volume of the gas will increase with
increasing temperature. The volume will decrease as
the temperature drops.

9. cold hot
Arrangement of particles in gas
•When the gas is heated, the molecules become more
energetic, move faster and are further apart. This
causes the volume of the gas to increase and expansion
is said to occur. At a lower temperature, the molecules
move very much slower due to less energy. They are
closer together, causing the volume to decrease and
contraction occurs.

10. •The effect of expansion and contraction of matter can
be very troublesome. Precautions have to be taken
against these effects. We can also apply the principle
of expansion and contraction of matter in making
instruments that are useful in our daily life.
•The following are some examples to show the use of
expansion and contraction of matter.

11. a. Mercury in a thermometer
- Mercury is a liquid metal that can expand and
contract when there is a change in temperature.
- This make it suitable for temperature
measurement and it is used in a thermometer.
Mercury in a laboratory
thermometer

12. Clinical thermometer

13. b. Bimetallic strip in a fire alarm
-An automatic fire alarm uses a bimetallic strip to
switch on the electric bell when there is a fire.
-The heat from the fire causes the bimetallic strip to
bent towards the contact point.
-When the bending strip touches the contact point to
complete the circuit, the fire alarm rings.

14. -An automatic fire alarm

15. c. Bimetallic strip as a thermostat
-The bimetallic strip is also used as thermostat in an
electric iron for controlling and maintaining
temperature.
-As temperature rises, the bimetallic strip bends away
from the contact point and cuts off the current.
-When the bimetallic strip cools down, contact is made
again and current flows once more to heat up the iron.

16. Thermostat in an electric iron

17. d. Bimetallic thermometer
-A bimetallic strip wound in a spiral can be used to
make a thermometer.
-In the figure below, the metals used are brass and
invar, with brass on the outside. As the temperature
decreases, the spiral is wound tighter and the pointer
will move to the left.

18. A bimetallic thermometer

19. •When laying railways tracks, gaps have to be left
between successive lengths of rail to allow for expansion
on the hot days. Without the gaps, the tracks buckles
and this affects the safety of the trains.
A gap in railway
tracks

20. •When concrete roads are laid down, gaps (normally
filled with bitumen) are left between sections in order to
allow for expansion on hot days.
Gaps between concrete sections

21. •Structures like steel bridges and overhead bridges and
built with gaps to allow for expansion . Sometimes,
one end is supported by rollers which allow the bridges
to expand easily when heated.
•Rollers of steel bridge

22. •Electric transmission cable and cable cars’ cable sag
on hot day and tighten during a cold night. Therefore,
allowances have to be made for the expansion and
contraction of the cables.
•Overhead cable sag in hot weather and tighten
during a cold night

23. Rivets
a.Rivets are steel pins used to join pieces of metal
slightly together.
b.They are heated before being inserted through two
pieces of metal.
c.While the rivet is still hot, the end is hammered flat.
d.When the rivet cools, it contracts, pulling the two
pieces of metal tightly together.

24. Stages of riveting

25. A very tight bottle cap can removed easily by immersing
it in hot water. The cap expand much faster than the
bottle and so, the cap can be removed easily when it
expands.
The hub of a wheel us usually slightly smaller than the
size of its axle. To fix the axle into the hub of the wheel,
the axle has to be put in liquid nitrogen (at -190 C) to
cool it so that it contracts until it can be fitted into the
hub.

26. •Metallic tires
The metallic wheels of a train are fitted with metal
tires. To ensure a tight fit, the tire is slightly smaller in
diameter than the wheel. Before fitting, the tire is
heated uniformly and the resulting expansion enables
the tire to be slipped over the wheel. Upon cooling,
the steel tire contracts and make a tight fit.

27. Fitting a metal tire onto a metal wheel

28. •All objects can absorb and give out (radiate) heat. But
some objects absorb or give out heat better than
others.
•The ability of an object to absorb and give out heat
depends on the type and color of its surface (dull or
shiny and light colored or dark- colored)
•The rate of which heat is absorbed and given out also
depends on the surrounding temperature of an
object.

29. •Most of the buildings and houses are painted with white
or brightly colored paint so that less heat is absorbed and
the interior can be kept cool. White and bright surfaces
are good reflectors of heat and poor absorbers of heat.
•The oil tank of an oil tanker is painted silver so that it
becomes good reflectors of heat. This is safer as less heat
will be absorbed by the petrol inside the tank. Oil storage
tanks are also painted with shiny aluminium paint to
reflect the radiated heat away so as to keep the contents
(oil cool).

30. •The base of the heating utensil or a pot is usually dull
and black. This makes it good absorber of heat.
Kitchen utensils