1. - When heated , solids , liquids and gas expand ( expansion)
- When cooled , solids , liquids and gas contract ( contraction)
- Some solids expand so little that we may not notice the expansion
Eg. 1 metre brass rod increase 1mm when heated and temperature increase by 100°c
- When cooking soup / boiling water , do not fill pot/kettle to brim because water expand
when heated and it will spill out
- Pg173 ( bottom )
- Holes in slice of bread because when a loaf of bread is baked , thousands of tiny air
bubbles are trapped in the dough . When dough heated , air bubbles gain heat and
expand , creating holes that causes the bread to rise .
- When body expands / contracts , large forces may be set up and it may help/hinder us .
- Pg175 ( top – experiment 5 )
- Large forces given rise and exerted from expansion .
Problems caused by expansion
Category Problem Solution Examples
Roads and Excessive Tiles on 1.Tiles pop out
Pathways expansion on very pavements and due to in sufficient
hot days cause walls are laid with expansion gaps
roads / pavements expansion gaps 2. Expansion gaps
to crack , tiles to help prevent tiles
pop out from getting
damaged
MRT and railway Railway tracks Gaps made in Distorted tracks on
tracks warp due to tracks to allow abandoned
expansion. expansion. railway due to
expansion caused
by heat .
Bridges and metal Long bridges Expansion gaps or Eg. Golden gate
girders expand up to a a free end resting bridge , Benjamin
metre in hot on rollers to allow Sheares Bridge in
weather and expansion / Singapore
without contraction
allowance , without damage
structures are at
risk of damage
Water pipes Water pipes/oil Expansion bends See pg177 ( top –
pipelines expand made to allow graphic )
and burst expansion
Telephone wires Raised on poles Strung loosely Transmission wires
and cables contract in cold from one pole to strung loosely .
weather and another pole for
become taut and contraction
may snap

2. Laboratory Boiling water Glassware at -NIL-
glassware poured into thick home and lab
glass , glass crack made of special
due to uneven glass unlikely to
expansion crack when hot
liquids are poured
in due to little
expansion when
heated .
Warp : to turn /twist/bent out of shape.
Uses of expansion ( pg. 178-179)
- Metal tyres :
 Metal tyre heated to fit over wooden wheel , tyre cools , clings on very tightly to rim of
wheel
- Rivets:
 Join steel plates and girders
 When red-hot , the rivet is put in position then hammered into a head and cooled,
contraction on cooling pulls steel plates together
- Bimetallic strip
 Rivet a strip of brass and strip of steel together , it is bimetallic strip
 Brass on top , steel below , rivets fasten both
 Brass expands more than steel when heated and strip bends with brass on outside
curve , when cooled brass contracts more than steel so strip bends with steel on
outside curve
Uses of bimetallic strips
- Thermostat
 Bimetallic strips used in thermostat, used to keep temp. constant
 Seen in ovens, refrigerators to keep temp. either hot / cold
 Pg. 180 ( top )
- Bimetallic thermometer
 Can be made into a long , nearly flat coil
 One end fixed and other end has a pointer
 Coil tightens or unwinds as the temperature goes up and down and pointer move
over scale marked in °C temp. degrees
 Uses uneven expansion to measure temp.
 Other thermometers pg.181 (top)
- Fire alarm
 Brass over iron and when fire occurs , heat cause brass to expand and bend in
towards iron and close circuit enables current to flow and activate fire alarm
 Pg. 181 ( bottom )

3. Questions
1. What substances expand the most when heated?
Ans:
2. What is bimetallic strip made of?
Ans: Brass and iron.
3. Pg. 183 (qn 7)
Ans: