If you place arrows on any location of a slime block, bound only to one side by a sticky piston, the following will occur:

• Arrow velocities are tightly bound to the direction of the slime block's movement, regardless of what velocity the arrow was prior.

-Arrows stuck to the bottom of a slime block, then the following slime block placed in any XZ axis movement will cause the arrow to propel in the direction of movement, rather than sticking to the slime block.