Physics is related to Force. Force is a type of Mass. Mass is related to Field. Field is related to Ground. 
Sigh is related to Air. you are likely to find Moon in/at/on Air. Moon is related to Natural. 
Physics <--RelatedTo--> Force --IsA--> Mass <--RelatedTo--> Field <--RelatedTo--> Ground 
Sigh <--RelatedTo--> Air <--AtLocation-- Moon <--RelatedTo--> Natural 