Good Question

上学途中，由于故事书里的 “烈日当空”和“艳阳高照”两句成语，妈咪一再解释好让承懿明白中文字的简洁和传神之处。就这样妈咪儿子的话题由太阳开始，演变成银河系里的行星。那一个行星最大啦、最小啦、离太阳最远啦。。。承懿使用的是英文名词，妈咪较熟悉的是中文名词，有点像鸡同鸭讲很混乱，妈咪差点要投降了。

就在妈咪的头变得很大的时候，承懿还抛出这么一个问题 ：
“Mom, the earth is rotating now, right? I wonder why we don’t feel it, not even a bit. Why? Can you please tell me WHY ?”….

哎哟! 天啊！饶了我吧！这么有深度又这么科学的问题叫我怎样回答？ 你妈咪我可是“科学零蛋”啊！唉！不答不答还须答。

“This is a very good question, Sam! Mommy is happy that you asked this question. Honestly, mommy does not know the answer. I am afraid that I might give you a wrong answer. Dad will be able to answer it. Please ask him tonight when he comes back….ok?”
“Alright….how come we don’t feel dizzy and will not fall? The earth is spinning….Is that because of atmosphere?”
“Err….I think it’s nothing to do with the atmosphere. I think it’s more to gravity. You know gravity, right? It pulls us down to the ground, that’s why we don’t fall….You please check with dad again. I am sure he will be happy to explain to you.”…

唉！我9岁儿子的脑袋到底在想什么？是不是男生才会相类似的 科学问题？我自己是从来不会有这方面的疑问的 （哈哈!朽木不可雕）。

后记 ：晚上爸爸回来吃晚餐时，承懿就丢了同一道问题给他。爸爸 听了笑一笑。饭后就上网。承懿做完功课后，爸爸就show 承懿网上的资料 （如下）。承懿到底明白了多少我不晓得。我只知道两父子在 我的netbook前交流了很久。。。

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How Fast Does the Earth Rotate?
Written by Fraser Cain

The ground feels firm and solid beneath your feet. Of course, the Earth is rotating, turning once on its axis every 24 hours. Fortunately gravity keeps you firmly attached to the planet, and because of momentum, you don't feel the movement – the same way you don't feel the speed of a car going down the highway. But how fast does the Earth rotate?
You might be surprised to know that a spot on the surface of the Earth is moving at 1675 km/h or 465 meters/second. That's 1,040 miles/hour. Just think, for every second, you're moving almost half a kilometer through space, and you don't even feel it.
Want to do the calculation for yourself? The circumference of the Earth at the equator is 40,075 km. And the length of time the Earth takes to complete one full turn on its axis is 23.93 hours. So 40,075/23.93 = 1,675 km.
The speed of the Earth's rotation changes as you go North or South away from the equator. Finally, when you reach one of the Earth's poles, you're taking a whole day to just turn once in place – that's not very fast.
Because you're spinning around and around on the Earth, there's a force that wants to spin you off into space; like when you spin a weight on a string. But don't worry, that force isn't very strong, and it's totally overwhelmed by the force of gravity holding you down. The force that wants to throw you into space is only 0.3% the force of gravity. In other words, if the Earth wasn't spinning, you would weigh 0.3% more than you do right now.
Space agencies take advantage of the higher velocities at the Earth's equator to launch their rockets into space. By launching their rockets from the equator, they can use less fuel, or launch more payload with the same amount of fuel. As it launches, the rocket is already going 1,675 km/hour. That makes it easier to reach the 28,000 km/hour orbital velocity; or even faster to reach geosynchronous orbit.