* No new substances are formed: The rocks and sand remain the same chemically. You're simply separating them based on size.

* The change is reversible: You could easily combine the rocks and sand again.

* Only the arrangement of matter changes: The screening process alters how the rocks and sand are arranged, but not their chemical composition.

Therefore, screening rocks from sand is a physical change, as it involves only a change in the physical state or arrangement of the substances involved.