|When you put a balloon filled with water over a
flame such as a candle, why doesn't the balloon
pop or burst?
The reason a balloon filled with air pops when
you put it over a flame is because the rubber of
the balloon gets very hot and weak and then
breaks. When you fill a balloon with water
instead of air, the water absorbs most of the
heat, so the rubber doesn't get very hot. Water
has a very high heat capacity, much higher than
air, so it will keep the balloon from bursting.
When you put an object over a flame, it starts
getting hot-- gaining heat that is released from
the flame.In a normal balloon filled with air, the
rubber of the balloon quickly heats, fraying and
coming apart-- so the balloon gets a hole and
pops. But if the balloon is filled with water,
the heat that the balloon rubber is gaining can
dissipate into the water inside, raising the
temperature of the water and leaving the rubber
surface cool and undamaged. This is because water
transfers heat much more efficiently than air, and
has a higher heat capacity (how much heat is
needed to raise its temperature).
Conduction: it takes a lot more energy to heat
up a volume of water than a volume of air, and so
the heat from the candle just goes into the water
and doesn't warm it up much. If the balloon is
filled with air, however, the heat goes into the
rubber, which causes it to fail and burst the
The skin (plastic) of the balloon is very thin,
so it gets cooled by the water inside. If you
held it over the fire long enough, eventually the
water would reach a temperature that was too high
for the plastic to survive, and then it would pop.
Water absorbs most of the heat from the flame so
that the surrounding rubber cannot increase its
temperature enough to melt (let alone burn).
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