Answer 1:
Well, let's boil this question down (see what I
did there?): the rate at which ice melts depends
on how quickly it's losing heat. Now, this heat
loss depends on two factors: the temperature of
its environment and how quickly its environment is
able to conduct heat away from the ice.
So, let's say you have two pieces of ice, one
just sitting out in air (at room temperature) and
one sitting in a glass of water (also at room
temperature). Now, the temperature of both
environments (the air and the water) is the same,
so the only think will determine which block of
ice melts faster is which environment is able to
conduct heat away from the ice. As you noted, the
ice floating in water will end up melting faster,
and that's because water is a much better
conductor of heat than air is.
But what if the temperatures of the environments
are different? Say you put one piece of ice in an
oven and another in room temperature water. Then
even though the water conducts heat better,
because the air in the oven is so much hotter, the
ice in the oven will still melt much faster. So
ice can melt faster in gas than in liquid, but it
just depends on the temperatures of the liquid and
gas!
Sebastian Fischetti
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Answer 2:
This is a great question! Something that we need
to consider is a property called the thermal
conductivity. This is a measure of how well a
material conducts energy through heat. The units
of thermal conductivity are watt per (meter
Kelvin), which is a useful way of saying how much
power (energy per time) can be conducted per
distance at a particular temperature. Looking up
values, we find that the thermal conductivity for
air is about 0.025 W/m•K, while that for liquid
water is 0.56 W/m•K. The value for liquid is over
an order of magnitude higher! Thus, we expect ice
to melt faster (transfer its energy better) in
liquid water than in air.
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