joi, 6 noiembrie 2008

Aerul

Omul poate supravietui cateva saptamani fara hrana, cateva zile fara apa, insa numai cateva minute fara aer. Aerul este esential pentru viata.

1.Ce este aerul?

Pamantul este inconjurat de o patura de aer, numita atmosfera.Aerul este alcatuit din 7 gaze.Unul dintre ele este oxigenul,de care oamenii si animalele au nevoie pentru a trai.Aerul este pretutindeni in jur, insa nu-l vedem.Il sintim doar atunci cand bate vantul.Vantul este aer in miscare

2.Aerul se intinde.

Aerul nu are forma.El este peste tot si se extinde in toate directiile.Daca umflam un balon tot mai mult aerul dinauntrul lui apasa atat de tare incat balonul va exploda.Cand o parasuta coboara .aerul care umfla panza apasa de fapt asupra acesteia,incetinindu-i caderea

3.Aerul cald se ridica.

Cand aerul din jur se incalzeste, se dilata si ocupa mai mult loc.Aerul cald este mai usor decat cel rece si se ridica deasupra lui.Baloanele cu aer cald se inalta deoarece sunt mai usoare decat restul aerului.Aerul din balon este incalzit cu combustibil.Cand nu mai este incalzit ,aerul din balon se raceste,iar balonul coboara.

4.Aerul tine cald.

Aerul poate tine de cald.Hainele de lana sunt mai calduroase deoare ce fibrele lanii retin mult aer.Iarna, pasarile isi infoaie penele pentru a retine intre ele cat mai mult aer,care le tine de cald.

5.Presiunea aerului.

Aerul apasa asupra noastra,dar corpul nostru este facut in asa fel incat nu-i simte greutatea.

In compozitia chimica a aerului, se remarca doua categorii de elemente: unele care se afla in mod constant si altele care se gasesc numai in mod accidental. Elementele constante ale aerului, oxigen (20,95%), bioxid de carbon (0,03%), si azot (78,09%), se gasesc in proportii aproape fixe, pe cand ozonul (1-2 mg la 100 m3), vaporii de apa, gazele rare (heliu, argon, neon, xenon etc.), amoniacul, oxidul de carbon (1-15 mg la m3) se gasesc in proportii variabile.

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