Okay! Did you know that cutting the wood is an example of a physical change?
I have to cut some more wood for the fire, then you can have your marshmallows.
Well now that is an example of a chemical change.
Oh no! My marshmallow burned.
Cutting wood is a physical change because no new substances were formed. It is still wood. When burning a marshmallow, the heat causes a chemical reaction, producing water molecules which evaporate, and you are left with carbon. New substances were added and formed.