Heating up the milk
Milk that has turned sour has undergone a chemical change. Lactose is converted to lactic acid which sours the milk.
Milk can be turned into - yogurt - cream - butter - cheese.
What are all these questions about physical vs chemical changes? Physical changes ARE chemical changes, and, conversely, chemical changes can cause changes in physical appearance and structure. They are fundamentally the same question.
I am not sure about the question connected to the changes of such type. But I am happy to work on this base with the reliable company where I order a lot of items to simplify my life and work.
I would say that it is a change in ph sure it looks like a physical change but maybe that is a side-effect of the ph changing to a hight acidity level and if you think about it why would we call it milk has gone sour if the ph did not change from a base to slightly more acidic (sour things are acidic)
Chemical change, it is decomposing, add enzimes to milk, and you can change it to cheese, or yogurt, etc.
Physical change!
Chemical change
A physical change it is still milk in the end