Ball in water in an accelerating elevator

[leetramp]

The weights on the spring are attached to a bar. When the elevator accelerates upwards, the mass is "left behind" and the spring stretches. When the elevator accelerated downward, the mass is again "left behind" and it appears to move upward.

The text tells you the motion of the elevator in the next portion of the video.

[kamalmichael]

looks very interesting but dont really understand ... Is the spring attached to the ball ?

Is the weight supposed to be the lift ?.... does the elevator go down first and then spring up to the second floor ??

[leetramp]

@kamalmichael The spring is hanging from a ringstand that moves with the same speed/acceleration as the elevator. The weights, having mass/inertia, stretch or slacken the spring as acceleration occurs. Since the elevator starts moving up from the first floor, the initial effect is for the mass to appear heavier, and the spring to stretch. When the elevator reaches the 2nd floor, the mass appears less heavy, and the spring slackens.