What is the rule determinating whether or not we need to capitalize them?
Sometimes I see "Math" ; "Physics" in the middle of a sentence, and sometimes lower case is used.
Generally, you should capitalise the names of school subjects only when you refer to a specific course:
I am excited to study history this summer.
I'll be taking History 101 at the community college.
But you always capitalise the names of languages:
- I am excited to study Russian this summer.