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Brady's been doing some science he
discovered that when he took ice from
his freezer and dropped it in his drink
the ice crack and he wondered why this
is an example of quite a common
phenomenon which is called differential
expansion when you drop ice into your
drink the drink is warmer than the ice
the outside of the ice warms up and
expands the inside is still very cold
he can't expand and so it just cracks
because part of its trying to get bigger
and part of saying the same so there is
essentially a tug-of-war between the
inside and the outside and it gives way
so the second thing Brady noticed was if
he left the ice on the plate in the
table for 10 minutes or so when you put
it in the drinks it didn't break and the
reason is that his freezer is cold
probably - 15 - 20 centigrade so when it
first comes out to the freezer the ice
is much colder than the melting point of
water so it's minus 20 degrees
centigrade and yet water warms it up
quickly
and causes the ice to expand
on the other hand if you leave it lying
around the ice warms up to its melting
point naught degrees centigrade and then
when you put it into the water the ice
doesn't expand it just melts
but then I asked Brady what did you
think would happen if we dropped ice
into liquid that was really cold so we
have hot ice compared to the liquid and
we can do that very easily by dropping
ice into liquid nitrogen which is at
minus 196 degrees centigrade so is very
very much colder than the ice and of
course he went to Neil and did the
experiment
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this time the outside of the ice instead
of expanding contracts because it gets
cold the inside can't contract quickly
enough so it shatters just in the same
way as it does in the drink
in fact it shatters rather more
dramatically than in water
you