21.为什么“作用力等于反作用力?Why the actin

2019-1-5

21.为什么“作用力等于反作用力?

答：因为力是由“双方数量相同的力线相互作用”形成，必定“大小相等、方向相反” 


(21)Why the acting force is equal to the reacting force?

Answer：because the force was formed by act each other of the force-line of both side, certainly “be equal in size and opposite in direction”