地心吸力那裡來

我想用表面表張力來解釋, 可能不對請指出.
每件物件由內到外有molecule 對molecule所以所有electrons forcesnuetralized. 但到表面時就有一面無野neutralized所以形成有surface tension向物件吸入去, 而地球表面就有此力叫地心吸力了, 是否這樣easy呢? 請大師們指教.

地心吸力來自地球自轉向心力？錯！
應該說，物件的重力成為和地球一起轉的向心力

The answer given in the above post is misleading.
Gravity doesn't come from centripetal force. In fact, the reverse is true. The gravitational pull of the earth provides centripetal forces to objects resting on earth surface.
"Force" is not equal to "energy". Gravity doesn't come from the "internal energy" of the earth. Instead, it comes from the "mass" of the earth.
The origin of gravity can be explained by Einstein's General Theory of Relativity, which he published in 1915. Simply speaking, any mass would make the space (and also time) around it to curve. This is called warpping of space. Since any straight line trajectory on a flat surface appears curved on a warpped space, thus an object travelling close to another larger (massive) object would appear to curve towards the larger object on the wrapped space. The is observed by us as gravitational attraction.
You may refer to the following web-page for details:
http://abyss.uoregon.edu/~js/21st_century_science/lectures/lec07.html
http://physics.suite101.com/article.cfm/gravity_and_general_relativity
The following youtube movie (~7 min) also shows a good illustration of Einstein's General Relativity and Gravitation. Pay particular attention to the last 2 minutes of the movie in which wrapping of space is introduced.
http://www.youtube.com/watch?v=tpbGuuGosAY

用較簡單的方法理解~
地心吸力來自地球自轉時產生的向心力~
(一直指向地心的合力~i.e.不只一種力~)

而這個向心力的F~
就是F = m x ω2次 x r
（註: r = 地球半徑, ω = 角速度, 物件在地球弧面上跟著轉動的速度）


既然向心力只是一些力的總稱~~
那麼來自哪裏呢~
(就像我們揮動一根綁住小石頭的繩~
小石頭之所以會有向心力是來自繩的張力~)

其實就是來自地球和地面物質之間的萬有引力~

萬有引力是指具有質量的物體之間的吸力(純粹因為質量而存在的引力)~
而萬有引力是自然界的四大基本交互作用之一~
也是最弱的~因此我們不會感受不到和其他物質之間有引力~
(因為大家的質量都太小~但去到地球的質量便夠大能感受到了~)

(註：另外三種是電磁交互作用, 弱交互作用及強交互作用~
電磁交互作用最簡單理解就是正和負電之間的吸力~)


因為不想說的太複雜~
所以只解到這類~~
(事實上有關萬有引力我也只知皮毛呢...)


如果想認識多點可以先從看維基開始呢~~

地球引力
http://zh.wikipedia.org/wiki/%E5%9C%B0%E5%BF%83%E5%BC%95%E5%8A%9B

萬有引力
http://zh.wikipedia.org/w/index.php?title=%E8%90%AC%E6%9C%89%E5%BC%95%E5%8A%9B&variant=zh-tw


Hope this helps~~ =]

2009-03-07 04:41:31 補充：
不是(一直指向地心的合力~i.e.不只一種力~)

應該是(導致物質一直指向地心的合力~i.e.不只一種力~)

2009-03-09 05:16:40 補充：
其實兩位高手的確說的沒錯~

但我只是想用一些單簡的概念去說明一下~
(因為以前學地心吸力也是從向心力學起~
而且一來便談及相對論這些的~
我也沒把握能夠自己掌握 + 說明得清楚~)

不過我也明白其實說"地心吸力來自地球自轉時產生的向心力~"
在物理學來說是犯了很大的錯誤...
我應該說"從最簡單的層面來說~地心吸力可用地球自轉時產生的向心力來理解~"

自問學物理只學了一段時間~
又大久沒碰過~
原本就不應該班門弄斧才對~
不過我想大家會在這裏~
不也是本著希望盡自己的能力為別人解答疑難的心嗎~~?

抱歉見笑了~~＞＜