Page 2 - Lesson notes- heat

Applications of change in dimensions on heating of substances:
Ø Small gaps are left between the railway tracks to accommodate the
expansions of the metal in summers.
Ø Thick walled glass tumbler cracks when boiling water is poured into it.
Ø Heating of milk sometimes overflow due to expansion in volumes.
Ø Hot air balloons rises up as hot air is lighter then the cold air.

NOTE:
The increase in size of an object on heating is called Thermal expansion.
Heat flow continues till both the bodies reach same temperature. This temperature is called
Equilibrium Temperature.

Some Pictures of Thermal Expansion:

Example-1 Intense heat causes steel railroad tracks to expand.

Example-2

In Summer (Hot Weather):

• The temperature increases.
• The metal wire gains heat and the atoms
vibrate more.
• This causes the wire to expand and
become longer.
• The wires may sag or droop between
poles.

In Winter (Cold Weather):
• The temperature decreases.
• The metal wire loses heat and contracts.
• The wire becomes shorter and tighter.

Example-3 Looping of metal pipes in industries.

ACTIVITY