Por que uma pessoa se encolhe ao sentir frio?
Autor: Professor Marcelot | Publicado: 2011-11-07T13:44:00-03:00

É comum em dias de baixa temperatura, procurarmos agasalhos adequados e se houver possibilidade nos locais onde estamos institivamente fechamos as mãos, cruzamos os braços, encolhemos as pernas e curvamos o corpo.Quando a temperatura do ambiente é menor que a temperatura do nosso corpo perdermos calor para ele, com isso sentimos a sensação de frio. Esta sensação que temos em dias de baixa temperatura ambiente é minimizada ao vestirmos roupas de lã. O fluxo de calor entre nosso corpo (quente) e o meio externo (frio) é reduzido pelo uso de determinado tecido na confecção das roupas.É importante frisar, que roupas e cobertores não "aquecem" ninguém. Eles somente aprisionam uma camada de ar ao nosso redor que passa a funcionar com um bom isolante térmico, impedindo a perda de calor do corpo para o ambiente.Pela lei de Fourier, em um regime estacionário de condução em que a propagação de energia térmica é constante através de um material condutor homogêneo, o fluxo de calor é dado por:Note que, o fluxo de calor que atravessa um corpo é diretamente proporcional à área da superfície exposta. Ou seja, quanto menor a área, menos calor pode passar pelo corpo em um intervalo de tempo considerado.A geometria métrica nos mostra que, para sólidos de mesmo volume, a esfera é a que apresenta menor área externa. Por isso, ao sentirmos frio, institivamente nos encolhemos, para uma aproximação com a forma esférica. Reduzindo a área de contato com o meio exterior, diminuímos a perda de calor para o ambiente.<!--[if gte mso 9]>           <![endif]--><!--[if gte mso 9]>     Normal   0         21         false   false   false      PT-BR   X-NONE   X-NONE                                                                                             <![endif]--><!--[if gte mso 9]>  <w:LatentStyles DefLockedState="false" DefUnhideWhenUsed="true"
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 <![endif]-->Fonte: Conexões com a Física/Blaidi Sant'Anna ...[et al.], - 1 e.d. - São Paulo: Moderna, 2010. v.2 - pág. 22.Fonte: Silva, Cláudio Xavier da. Coleção física aula por aula;&nbsp; São paulo: FTD 2010. v.2 - pág. 152.&nbsp;