today I want just to
think what would happen if ice instead
of floating on the surface of
water sank to the
bottom imagine in the winter when your
pond in your garden or in the park froze
the ice when it Formed would go to the
bottom and then as more and more ice
built up the layer of ice at the bottom
would get thicker and thicker until in
the end the pond would be nearly totally
Frozen and all the fish would be forced
up onto the surface and would be
squirming around on the surface till
birds at them or fishermen just pick
them up or if you were at Sea with a
nuclear submarine if the sea started
freezing it would be most embarrassing
your submarine could appear on the
surface of the ice and you'd be the
mercy of whoever you wanted how was is
that different from the the way it is
now except the fish gradually gets
squashed to the bottom as it gets
thicker and thicker now the ice forms on
the surface and when it forms on the
surface it forms quite a good insulating
layer and eventually if you're really
unlucky the ice could form all the way
down and squash the fish at the bottom
but that doesn't usually happen because
ice is a really very good insulator and
so most places unless it's really cold
like in the Antarctic or somewhere like
that there will be liquid water at the
bottom even in the Antarctic there are
underground lakes that have recently
been discovered where there's liquid
water right at the bottom as you go
deeper the pressure goes up and when you
go down at low depths the pressure is
higher and the melting point of water
actually goes down as the pressure
increases now the the question is why
does it happen why does ice float on the
surface of the
water and the answer is that the water
molecules in ice are actually joined
together by so-called hydrogen bonds
these are bonds of oxygen hydrogen
oxygen and they are in a very regular
crystal structure when you melt ice
these bonds break not all of them but
quite a few of them so you still have
some of the water molecules joined
together but in a very random and H
Hazard way so instead of having a very
regular crystal structure with the bonds
between oxygen hydrogen and oxygen they
collapse and so the density gets
higher so ice is not very much lighter
than water but it's light enough to
float that's why just the tip of an
iceberg sticks
out if ice was denser than water
icebergs would just fall to the Bottom
of the Sea you wouldn't have the film
Titanic it would have enormous effects
on our planet if ice did not
float because ice as you know is white
and so it reflects sunlight so when the
sea
freezes and forms sea ice
this reflects back a lot of the
radiation from the
Sun and particularly in areas like the
Arctic in summer where it's daylight 24
hours a day the reflection of the sun's
radiation by sea ice is really quite
significant sea ice floats particularly
well because it is pure ice but it is
floating on salty water which is denser
than ordinary water and and therefore it
is particularly buoyant if you stop
reflecting so much of the sunlight that
has implications for the whole of the
earth's climate because more radiation
is absorbed by the Earth it will get
warmer and therefore more ice will melt
and so on so if ice didn't
float the our planet would probably be a
considerably warmer place than it is now
of course the place where most people
see floating ice are in their drinks now
it's quite important when you drink at
least particularly at the beginning you
drink from the top of your glass so you
want the first part of your drink to be
really nice and
cold and as you chat away and tell
stories and so on the glass goes down
and so you're always drinking from the
surface so
so if you put ice cubes into a drink and
they sink to the
bottom you end up with a warm
drink and that would be a social
disaster alcohol pure
alcohol is much less dense than water
and I just have a
feeling that if you take ordinary
ice and put it into pure alcohol it
would sink to the bottom we'll have to
try the
experiment we're in the vault The bullan
Vault of the bank of England and I'm
really excited I've never seen so much
gold in fact I've never seen so much of
any
element