Simplify the following text for a Grade 9 native English-speaking person.
Original: It is a branch of continuum mechanics , a subject which models matter without using the information that it is made out of atoms , that is , it models matter from a macroscopic viewpoint rather than from a microscopic viewpoint .
Simplified: It is a branch of continuum mechanics , a subject which models matter without using the information that it is made out of atoms .