这时我想起了一个笑话,大热天,一个财主躺在大厅里的凉床上乘凉,可是浑身还是汗流不止。他唤仆人来给他扇扇子。过了一会儿,他遍体凉爽,一摸汗水都没有了。财主奇怪地说:“咦,汗到哪里去了?”仆人指着满头大汗说:“老爷,汗都跑到我身上了。”
是啊,我的汗跑到哪里去了?为什么电风扇吹出的风是凉爽的呢?带着这个问题,我查找了书籍和网络,终于得出了答案。
原来,人的皮肤表面都是潮湿的.,尤其在天热的时候,我们会出很多汗。风是空气流动的现象,空气有温度,但是风是没有温度的。电风扇只能加速空气的流动,从而形成风,但是风却不是凉的。空气的流动会使液体挥发的更快一些,当风吹到我们的皮肤时,皮肤表面的液体就会挥发成气体,这样会带走一些热量。汗液的挥发把我们皮肤表面的热量带走了,我们怎么会不凉快呢?
为了验证这个道理,我和妈妈又做了一个实验。把一块干燥的铁块对着风扇吹,它的温度并没有变化。我们用湿布在铁块表面涂了一层水,然后再放到电风扇前吹。铁块表面的水很快挥发掉,而用手触摸铁块,可以明显感觉到铁块的温度下降了。因为液体的挥发带走了铁块的热量。
弄懂了这个道理,我很高兴。我又进一步明白了物体变化的三种形态。
物体有三种形态,分别是液体,固体和气体。比如说水,它的液体形态是水,固体形态是冰,气体形态是水蒸气。把水放在零度以下的地方就会变成冰,放在锅里煮就会变成水蒸气。而从冰到水和从水到水蒸气都会吸收并带走热量,所以才有了“下雪不冷化雪冷”的说法。
真是身边处处有科学啊!
那天,天阴森森的,只有朗朗读书声传出教室。放学了,我和一些朋友来到食堂吃饭。但是我和我的朋友引发了一件恶劣的事情。食堂里同学们窃窃私语,人人脸上洋溢着欢乐的笑容,都文明地吃着饭。
我坐在了自己的\'位子上,和同学们谈笑风生,郑?辰坐在我旁边,和我们说说笑笑,他没坐在自己的座位上,坐在了余子尖的位子上。过了许久,余子尖来了,他愁眉苦脸地让郑路成离开他的位子,当他的火已经发到了极点后,他忍无可忍地把汤坚决地洒在了郑路成的脸上,郑?辰的头发像洗了头似的,全湿了。
郑?辰也去泼余子尖,我在一旁站了起来,去掐余子尖的脖子,余子尖也大呼小叫的叫着,其他同学没有像我一样和余子尖吵的,只有我、郑?辰和余子尖在一起互相大骂。我还去推余子尖,但余子尖始终没有还手。
余子尖,我真想对你说:“对不起。”但每当见到你,我就不敢对你说,心似乎受了控制一样,但是我在今日终于鼓起勇气向你说了一声:“对不起。”虽然雨依然下着,但是我和你的友谊地久天长。
Dear Frank:
I am terribly sorry to tell you that I have lost the valuable book you were so kind to lend me last week. I read it everyday and intended to finish it next month. Last night when I came to my room, it was nowhere to be found. I will try to recover it as soon as possible. If I fail to find it, I will get a new book for you.
But I am afraid it can never take the place of the old one. Old books are like old friends. Once lost, they can never be replaced. They are connected with cherished associations which the new ones can never have. And for this irrecoverable loss, I am to blame. I was so careless with my things. This is a warning to me to be more careful in the future.
Yours truly,
Tom
Dear Miss Morgan,
(1 I am so sorry to tell you that I won’t be able to attend the lecture on American history tomorrow afternoon. (2 Now, I’m writing this letter to show my deep regret (3 I do hope you can understand me and excuse me for my absence.
(4 I will be very grateful if you are kind to listen to my explanation. (5 The reason for my absence is that my uncle is returning home from France, and I have promised to meet him at the airport at 3:30 tomorrow afternoon. (6 Therefore, I will have to give up attending your lecture tomorrow afternoon.
(7I wonder if it is possible for lecture to be recorded, and if so, could I borrow the tape? Sincerely yours Li Hua
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