* Oobleck is a mixture, not a new substance. It's simply cornstarch and water combined. The cornstarch particles don't chemically react with the water to form something entirely new.

* The change is reversible. You can easily separate the cornstarch and water by letting the oobleck dry out. The cornstarch will remain cornstarch, and the water will evaporate.

* No new substances are formed. The cornstarch and water maintain their chemical identities even when mixed together.

In contrast, a chemical change involves the formation of new substances with different chemical properties. For example, burning wood is a chemical change because the wood reacts with oxygen to produce ash, carbon dioxide, and water.

Let me know if you'd like to explore other examples of physical and chemical changes!