As picture below, I want to explain why the bottom of spring will be
motionless a little while after release.

But in my view, the bottom of spring will be falling in a low speed after release, since the spring will become short after release, so the gravity will be greater than elasticity in the bottom, so the bottom will fall. But in picture below, seemly, the bottom of spring is motionless. How to explain it?

enter image description here