我想問咩叫newton's third law

newton's third law

即係A物件有任何的作用力施加於一件B物件上，B物件必有另一個，

相等力度，但係方向相反的力俾番A物件

有一樣野叫action and reaction pair.

好易學， the force acting on B by A

咁reaction 果個force 就叫　force acting on A by B

要睇acting on 邊個 by 邊個。

假設有個人企左係度，weight 係 the force acting on the person by the earth

佢相對的反作用力，應該係 the force acting on the earth by the person

但係normal reaction又係咩事呢？ normal reaction 係講緊個 ground！

注意～係ground。　normal reaction: the force acting on the person by the ground

而人俾番個地下，ground的force 係 the force acting on the ground by the person

只要睇下個名就知係唔係action- reaction pair

咁其實ground 同 earth 有咩唔同呀？

ground 係講緊果個面！ 人同呢個面有接觸，所以果種力係

force in contact!　CONTACT接觸

人作用係ground 的力，係一種push<<<認同嗎？

個腳板踩住個地下，push緊佢，個地下又push!番你

但係地球有咩唔同！？地球俾你的force 係～ force at a distance

你店唔到個core的～而且，呢個係一個 pull ! pulling force~

咁人作用係地球果個pulling force呢？點解睇唔到架呢？

咁～就要拎番條newton's second law出黎！！

假設你mass= 10 kg架姐~咁net force = ma ~你個weight就係10~

net force = 100N ~即係你個weight係100N

係呢個moment~~~ 黎番條newton's third law~

你作用番俾地球個力~same magnitude~opposite direction~

oh~~得100N~ 諗下先~咁地球幾重呀? N咁重-0-重你唔知N咁多倍~

再整番條newton's second law先~

net force = ma ~ 100 = N咁大既mass 乘 acceleration~

咁移一移個位 a = 100 / N咁大既mass

咁a係唔係好細先~? 所以點解個你跳高左，個地球拉你~你個a咁大～

而個地球郁都唔郁～係唔係我根本冇reaction force俾佢架？

答案＝唔係～係地球個mass 太大，acceleration細到唔知點整～

我地feel唔到～　所以先成日以為normal reaction and weight is action and reaction

記住～用action - reaction pair~ on乜乜by乜乜

咁就唔會錯架喇^^~

講左好多題外話添．．．希望幫到你啦，詳細ｄ，希望你會知清楚ｄ

newton's third law 是指作用於2物件之上的力，即A以力碰撞B，B會以同樣的反作用力實施於A之上。
留意力的方向與實施，是作用向不同的物件(力即向B，反作用力向A)

但normal reaction 是地面作用向物件
而weight 是地球作用向物件

以上二力都作用向物件，故不能成為action and reaction