Page 23 - Curriculum Visions Dynamic Book. To close the book, close the tab.

other solids. The fact that ice soaks up a lot of heat before it melts explains why ice packs are good for keeping things cool and why icebergs take such a long time to melt when they float into warm oceans.
Ice is only nine-tenths as dense as water because of the way ice forms into a network of crystals as it freezes. The expansion during ice formation
has important results
in many places. It
explains why exposed
water pipes burst on a
cold winter night, why
bottles of water put
in a freezer crack, and
why blocks of rock are loosened from cliffs during the winter.
The melting temperature of
ice goes down as more pressure
is applied. This has important effects. It is well known that it is easy to skid on frozen roads. This is because ice has low friction,
or stickiness. When ice is under pressure, for example, from the weight of a car tire or the blade
of an ice-skater, it melts and turns to water. The water then acts as
a lubricant, causing the skidding. Glaciers move over their rocky beds for the same reason. (See also: Crevasse.)
Ice Age
A period when the world’s climate cools, and glaciers surge down from mountains to form ice sheets. At present, glaciers and ice sheets have shrunk back, but it is likely they will eventually grow again. (See also: Fjord; Lake; Waterfall.)
 Ice crystals—This is a snowball made from compacted ice crystals.
 Ice crystals—A representation of the atomic structure of ice.
 Ice crystals—Ice crystals are typically six- sided or have six points.
Ice crystals
Water molecules are made of hydrogen and oxygen atoms.
The molecule is arranged with
one hydrogen atom at one
end, the oxygen and the other hydrogen atom at the other end. The molecule is shaped just
like a dumbbell. The hydrogen
end has a positive charge, while the hydrogen-oxygen end has a negative charge. Because of this water molecules attract one another end to end. The attraction is called hydrogen bonding.
The shape of an ice crystal is due to these end-to-end links. The links make six-sided (hexagonal) rings of water molecules, and that is why ice crystals have six points.
The arrangement of water molecules in ice does not allow any space for any materials that were dissolved in the liquid water. As
a result, these dissolved materials are ejected as ice forms, and
even seawater (which contains much salt) produces pure ice. Indeed, the freezing of water
can be used to make drinking water from seawater (a form of desalinization).
Ice is a brittle solid. If it is struck with a hammer, it shatters. However, if pressure is applied for a long time, the ice will begin to change shape, and in the case of glacier ice it will flow like syrup.
Given enough time, each of the hexagonal layers of molecules in an ice crystal can glide past one another. Furthermore, in places where the ice pressure is extreme, such as where the ice rests on the bed of a glacier, the ice will melt, providing water for lubrication.
The greater the pressure, the more the sheets of molecules glide, and the faster the ice flows. As
a result, the ice near the bottom
of a glacier flows faster than
the surface ice. The surface ice, which is not under much pressure, cracks, resulting in the formation of crevasses.
Ice crystals
23