Expansion and contraction · Alberta Grade 6 · maddyhelps.com
Name
Date
For each situation, write whether something is being heated or cooled, and whether it expands or contracts. Then explain one using the word particles.
What happens
Heating or cooling?
Expand or contract?
Concrete sidewalks are poured with gaps between the slabs.
A tight metal jar lid loosens under hot tap water.
Power lines hang lower on a hot summer day.
A balloon taken outside at −20 °C shrinks.
The liquid in a thermometer rises.
Explain one of them using the word particles
Why do bridges have metal joints with gaps in them?
Ice floats on a lake in winter. Why — and why does it matter to the fish?
For the grown-up
Hot and cold
“Concrete sidewalks are poured with…” heating, expand; “A tight metal jar lid…” heating, expand; “Power lines hang lower on…” heating, expand; “A balloon taken outside at…” cooling, contract; “The liquid in a thermometer…” heating, expand. Heated particles move faster and spread out, so the material takes up more room; cooled particles slow down and pack closer. Bridge joints leave room for the bridge to grow in summer and shrink in winter without cracking — Alberta's range from −40 to +35 makes them essential. Water is unusual: it takes up more room as ice than as liquid, so ice is less dense and floats. The floating sheet of ice insulates the water underneath, so the lake does not freeze solid and the fish survive.
The sidewalk gap is the example children remember, because they walk over it every day. Summer heat makes the slabs longer; without a gap they push against each other and crack.