點解個波有彈力?

inelastic係唔存在既，係ideal situation

elastic係源於intermolcular force of particles..........電磁力electromagnetic force

如果有外力加入，particles就會pull apart(就會造成形變)，咁就會將energy 轉做 potential energy of electromagnetic force ，然後 release番出黎(when外力消失)，就會有方向相反既力形成(形變消失)

咁就係elastic最簡化既解法

this is the problem about FORCE(力學).

Newton(牛頓)said that force always occurs in a pair.

There are action force(動力) and reaction force(反射動力).

When you push the ball to the ground,

the force from you and the active force(地心吸力--force of gravity)

will make the ball downward,

but the reactive force from the ball will make it upward.

The ball will contiune to upward and downward

until the action force and reaction force opposes(抵消) each other.

Then the ball will stop its motion.

i am F.2.. i don't know if it is correct.. i just tell you about what i learn