Thermal Expansion
Learning Objective:
|
Recognize the effects temperature, pressure, and salinity have on the
thermal expansion of seawater, and identify one of the major roles of
thermal expansion in the sea.
|
Liquids expand and contract when temperature changes take place; some more
than others.
Seawater has a higher coefficient of expansion than that of freshwater.
Within the sea, the coefficient of thermal expansion is effected by salinity,
temperature, and pressure. It is greater in high salinity water; greater in warm
water than in cold (under similar salinity conditions); and it increases with
increasing depth under constant temperature and salinity conditions. Of course,
constancy is not a trademark (prerogativa) of any of these properties;
they are all quite variable. In turn, the thermal expansion that takes place in
the sea varies and is difficult to assess.
A major role of thermal expansion is in the formation of ice. PURE WATER is
most dense at 4°C. Thermal expansion takes place when water warms above 4°C,
but it also expands when it cools below 4°C. When expansion takes place, the
volume is increased, which in turn decreases the density. When water cools below
4°C, it expands slightly, and as it freezes, it expands much more. If water
failed to expand during the freezing process, the density of ice would be such
that it would sink to the bottom on forming. In the cold of winter, freshwater
lakes would eventually (infine) become solid blocks of ice. Come summer (giunta
l'estate), only the upper few feet of ice would melt, leaving the remaining
ice beneath the melted water.
|
