在地球上,無重力狀態如何產生?

It can be happened when you are having the 降傘. Before you open the 降落傘,
when you falling is fast enough to reach the terminal velocity, then you will under
Free falling, which the the force acting on you is zero.
The gravitaion force (重力) is balanced by the upward force cause by the friction of the air
You seems not feeling any force acting on you. This state is the state you asked.
As the p3004962 said, it is 失重 instead no gravitation.
Hope this can help you. :)

多數(可能只能)係利用飛機從高空俯衝而下，係機內可維持約兩三分鐘失重狀態，記住係失重而唔係無重力，當時你係連人帶機一齊跌落去。