Quantas Gotas ainda cabem? Tensão superficial da água
Autor: Rafael Arenhaldt | Publicado: 2010-11-02T16:50:00-07:00

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GISELE MAURILDA DOS SANTOSLUANA PORTILLA DE MELLO
QUANTAS GOTAS AINDA CABEM?TENSÃO SUPERFICIAL DA ÁGUA
OBJETIVOO objetivo deste experimento é a utilização de técnicas para se perceber a tensão superficial da água líquida, assim como criar condições para que o aluno investigue situações em que a mesma será parcialmente rompida. MATERIAIS E REAGENTESÁgua
Copo
Conta-gotas
Jarra      
PROCEDIMENTOColocar      água em um copo até sua borda.
Após      fazer uma enquete com os alunos de quantas gotas de água ainda cabem      naquele copo, inicie a colocação das gotas e a contagem.
QUESTÕESO      que aconteceu?
Qual      a propriedade da água que este experimento apresentou?
Por      que couberam tantas gotas no copo que já estava praticamente cheio?
&nbsp;COMENTÁRIOSDesde o início foi-nos ensinado que a matéria pode estar em três estados bem definidos, sendo esses três estados: sólido, líquido e gasoso. Quando temos certa quantidade de água exposta ao ar, temos dois estados bem definidos, isto é, no seio da água o estado líquido e acima da superfície da água, o estado gasoso. Mas no limite que une estas duas fases, existe uma interface, à qual estão associadas propriedades totalmente diferentes das do estado líquido ou gasoso. Ao analisar as interações inter-moleculares que uma molécula sofre no seio da fase líquida, pode-se tirar a conclusão que essa molécula é atraída e repelida de maneira a que a resultante das forças seja praticamente nula. Uma molécula na superfície sofre atrações para o seio do líquido, mas no sentido contrário não sofre qualquer força. Isso vai implicar que na superfície de água existam forças não compensadas, fazendo com que a área da superfície seja mínima. Esse fenômeno é chamado de tensão superficial. A tensão superficial é definida como uma força contrativa que opera no perímetro da superfície e que a tende a comprimir.&nbsp;&nbsp; O que se pode observar é que as interações entre as moléculas de água da superfície e as que estão logo abaixo impedem que o líquido transborde. 
REFERENCIAL:ÁGUA: livro do professor/ Centro de Pesquisa e Desenvolvimento da Sangari Brasil. 10ª ed. São Paulo: Sangari do Brasil, 2007.