作用力和反作用力

1.例子：
(1)游泳時,人施於水的力(將水向後推)及水施於人的力(將人推往前)
(2)月亮施於地球的引力,及地球施於月亮的引力
(3)地球施於人的重力,及人施於地球的重力

2.你所說的兩個力,＊ 絕不是一對作用力和反作用力＊
在解釋上,要先清楚一對作用力和反作用力的條件
根據牛頓運動第三定律,一對作用力和反作用力是(1)量值相同(2)方向相反
**(3)作用在不同的物件上
＊留意:人的重量是地球施於人的重力,即是作用在人身上的力
而地面承托人的力,亦是作用於人身上的力!
由於不符合(3)的條件,這對不是一對作用力和反作用力...!!!

3.例子(3) ^ ^ (任何物件之間都有引力,我們也會有一種力吸引著地球,只不過是因為地球的質量比我們大很多,所以不會明顯地察覺到)

4.地面承托人體的力,及,人體施於地面的力

面對作用力和反作用力的問題是,形成的3個條件是關鍵!
＊特別是地心吸力給人的錯覺~
即使量值相同，方向相反，更要留意施予此力及受予此力的物件！＊＊＊

－－－－－－－－－
可能長氣了一點！＾＾""不過這方面的慨念一定要十分清楚才可以將問題迎刃而解!
希望你看過後,對這方面的問題,更可清楚了解!＊＊

solution to Q1.
a.walking- your foot exerts a force on the ground and the ground pushes you forward
b. rocket launching- a lot of gas is emitted downwards from the rocket. The rocket exerts a force on the gas, pushing it downwards. The gas pushes the rocket upwards.
c. firing a bullet- the gun/rifle exerts a force on the bullet and the bullet exerts a reaction force on the gun, resulting in the recoil motion of the gun.
Solution to Q2
weight and normal reaction is not a action&reaction pair. Weight refers to the gravitational force pulling you towards the centre of earth.
when your body(feet/shoes) is in contact with the ground surface the particles of the ground and your feet repel each other, leading to an action and reaction.(just like a head-to-head collision of 2 cars)
Solution to Q3
You are pulled towards the centre of the earth (ie. weight). And you also exert a force on the earth(towards yourself), like magnets attracting each other.
However, the force is too small to notice(negligible).
Solution to Q4
mentioned in Q2