Bronium

I have fallen in love with physics (class) once. Currently, we were on the topic of forces and I don't particularly like forces. I see them everyday. Nothing new or exciting. But then I got to thinking, why do we consider a body of mass to be one object? It's comprimised of other atoms and molecules and other stuff and they aren't even touching! So why do we consider them to be one thing? And shouldn't we be calculating the force on every single particle( I know sometimes...