Scenario:

A 2kg object is suspended by a string from the ceiling of an elevator.

Question:

Why does the tension reduce when the elevator accelerates downward (by 1.4 m/s^2) and increases when acceleration upward (1.4m/s^2)?

I understand that when in const velocity (down or up for elevator), Ft=Fg. Though, I don't fully why tension decreases when motion is downward and increases when motion is upward?