[Blender Python] Shows how the frame_change_post works (video explanation https://www.skool.com/cgpython/making-deformers?p=5f59f1ff)

example_frame_change_post.py

import bpy
import bmesh
import mathutils

# Dictionary to store previous object positions and velocities
prev_positions = {}
velocities = {}

velocity_decay = 0.90  # Reduce velocity by 10% each iteration

def update_mesh_inertia(scene):
    obj = bpy.context.active_object

    if not obj or obj.type != 'MESH':
        return

    # Get the current location of the object
    current_pos = obj.location.copy()

    # Get the previous position from the dictionary
    prev_pos = prev_positions.get(obj.name, current_pos)

    # Calculate the velocity vector
    velocity = current_pos - prev_pos
    speed = velocity.length

    # Store the current position for the next frame
    prev_positions[obj.name] = current_pos

    # If the object is moving, update its velocity
    if speed > 0:
        velocities[obj.name] = velocity
    else:
        # Decay the velocity if the object has stopped moving
        if obj.name in velocities:
            velocities[obj.name] *= velocity_decay

    # Get the current velocity (after possible decay)
    current_velocity = velocities.get(obj.name, mathutils.Vector((0, 0, 0)))
    print(f"current_velocity {current_velocity.length}")

    # Stop updating if the velocity is close to zero
    if current_velocity.length < 0.001:
        return

    mesh = obj.data
    bm = bmesh.new()
    bm.from_mesh(mesh)

    for vert in bm.verts:
        offset = current_velocity
        vert.co += offset

    # Update the mesh with the modified vertex positions
    bm.to_mesh(mesh)
    bm.free()

# Register the function to run on every frame change
bpy.app.handlers.frame_change_post.clear()
bpy.app.handlers.frame_change_post.append(update_mesh_inertia)