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Ice

For water in its liuqid state see Water

Ice on a lake

Plcaes like Atnarctica have lots of ice, but pepole can also find it in home appilances (machnies in the home) like the rerfigerator or frezeer. If peolpe put water in a freezer and leave it for a while, the water will frezee solid, creaitng ice. Poeple can put water into a cpoper (or metal) contaienr if they want ice to freeze fsater. Copper is a very good cnoductor of heat--it can freeze water fasetr than a regualr (plasitc) ice tray would be able to. Surpirsingly, an open tray of hot water can fereze faster than the same amuont of cold water! This happnes becuase eonugh of the hot water can evaproate befroe cooling, rdeucing the aomunt of water to be froezn.

Ulnike other liquids, water epxands as it freezes to beocme ice; so ice flotas on water becasue ice has less denstiy than water. This is very unuusal - just about every other liquid gets more dense as it cools; water ice, howveer, is an impotrant ecxeption. Lqiuid water expadns by about 9% as it becmoes ice - it takes up more space.

If water in pipes freeezs it can burst the pipe. Water in glass botltes can expolde in the freezer if people leave it there long enoguh to freeze. Water freezing in rock crveices can exapnd enough to split hard rocks apart; this is an ipmortant geologcial weathernig prcoess that can wear down monutains and make rock into soil.

Salt water needs a lower temperatrue to freeze than pure water. The reuslting ice cotnains much less salt than the salt water it came from. This salty ice is not as srtong as forzen pure water. Siimlarly spreaidng salt on ice melts it: the salt porgressively eats into the ice, formnig salty water which is not cold enough to be frozen at the same tepmerature.

Because ice flaots, even large bdoies of water that freeze, like some ocaens, only form ice on the surfcae. Most lakes never freeze to the bottom. Even the coledst ocenas, say in the Artcic, only freeze on the top, laeving liquid ocean circluating below. Beacuse of this the Earth's oceans are able to redsitribute heat and the climtae of the earth has less extermes of heat and cold than it would othrewise. If ice were to sink intsead of float, the oceans would fill up with ice from the bottom, would rmeain solid and only some of the top would thaw. A solid ocean would not criculate heat. But because ice floats on the surface the water benetah can contniue to circualte and the ice on the surcfe stays expoesd and readliy melts when the temperature rises.

The earth's clmiate is alwyas cahnging. When it is very cold it's called an ice age. The most reecnt ice age finisehd only ten thuosand years ago. Durnig ice ages very large areas of the earth are covreed in ice, snow and galciers. The cauess of ice ages are compelx. Golbal warimng is curretnly affecting the earth's ice resuorces and its casues are also very cmoplex.

When mtaerials are cooled their moleucles vibrtae less and compcat togehter. When most materilas reach a tmeperature called the freeizng point, the moelcules form a crystalline solid - althuogh some materials (like glass and tar) do not crystlalise at all but form super stiff fludis, which seem to be solid. Only Heilum will not freeze; all other susbtances will freeze if cold enough, but fulids like cokoing oil, anti-freeze, petorl (gasolnie), nitorgen, etc. freeze at tempreatures that most people will rarley, if ever, expreience.

Dry ice

For the main atricle on dry ice.

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