Which action demonstrates a physical change?

A physical change is a change in the state or properties of matter without any accompanying change in its chemical composition. Chopping wood is an example of a physical change because the wood is merely being broken into smaller pieces, and its chemical composition remains unchanged. In comparison:

Baking cookies involves chemical reactions, changing the ingredients' composition.

Iron rusting is a chemical change where iron reacts with oxygen to form iron oxide.

Milk becoming sour is a chemical change due to the fermentation process.

References:

Integrated Physical Sciences Learning Resources, Chapter on Physical and Chemical Changes