* No new substances are formed: The coca powder and water simply mix together. The individual components (coca powder particles and water molecules) remain the same. There's no chemical reaction happening that creates new compounds.

* The change is reversible: You can separate the coca powder from the water by letting it settle and then decanting or filtering the water.

* No energy change (significant): While there might be a slight temperature change due to the mixing process, it's not a major indication of a chemical reaction.

In contrast, a chemical change would involve:

* Formation of new substances: This is due to the breaking and forming of chemical bonds.

* Irreversibility: The change is difficult or impossible to reverse without another chemical reaction.

* Energy change: Chemical reactions often involve the release or absorption of heat (exothermic or endothermic reactions).

Let me know if you'd like more examples of physical and chemical changes!