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冰的体积变大还是变小?

在物理小组活动的时候,小明提出了这样一个问题:“水在结冰的时候体积如何变化?”小刚立即做出了回答:“根据物体热胀冷缩的性质,水结冰时的体积当然是变小的。”但小红提出了相反的意见:“如果体积变小的话,那么冰的密度会变大,冰将会沉入水中。但事实上冰会浮在水面上,所以体积应变大。”

到底谁对谁错呢?小刚提出了通过实验去解决这个问题,并提出了自己的实验方案:“在小药瓶中装满水,放到冰箱中使水完全凝固,然后看看冰面是下降了还是升高了,不就行了吗?”大家都赞同这个方法,于是他们立即动手实验。于是他们在小容器中装满水后放入冰箱让它结冰,结果发现冰面是向上凸起的。

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Protect Children from Cyber-bullying

    When you think about bullying, you might think of a child being bullied by another in the schoolyard. As more young people have access to computers and cell phones, traditional bullying has gone digital, which has not yet gained awareness in Chinese parents.

    Cyber-bullying, first invented by Canadian educator Bill Belsey, is the use of the Internet and related technologies to harm other people, in an intentional, repeated, and unfriendly manner. It involves threatening text messages, the spread of online rumors on social networking sites, and intentionally keeping someone out of an online group. Cyber-bullying is at an all-time high in the US. According to a study from the US Department of Justice, more than 43% of teenagers report being victims(受害者)of cyber-bullying.

    Compared to face-to-face bullying, cyber-bullying is considered to have a worse emotional effect on the victims, and kids could feel more desperate and depressed. Severe, long-term or frequent cyber-bullying can leave victims at greater risk for anxiety, depression, and other disorders. Research says that cyber-bullying victims were almost twice as likely to have attempted suicide compared to youths who had not experienced it.

    In traditional schoolyard bullying, at least home is a safe place for the victims. But cyber-bullying is endless---it could happen anytime. Moreover, in the digital world, bullying is much easier, as a bully can pick on people with a much lower risk of being caught.

    Actually, cyber-bullying has become a worldwide issue. In the US, as several teens committed suicide because of cyber-bullying, some schools set rules to punish cyberbullies. Laws to punish cyber-bullying have been introduced in some states. In China, cyber-bullying is still considered by many parents and educators as a problem that involves physical contact. However, as cell phones and laptops are becoming common equipment for teenagers, social interactions have increasingly moved from personal contact to virtual contact. Cyber-bullying is spreading faster than expected.

    For schools and parents, safety rules should be set in the virtual world for kids, such as telling them not to let out anything to a stranger. Active steps should be taken to make the public aware of the seriousness of this problem, because it would be too late to take measures after tragedy strikes.