fall apart
No object
Break into pieces, or fail
The old chair fell apart when he sat on it.
No object
Nothing follows the particle directly. You cannot say it with a direct object.
Related idiom
Read the meaning and origin of a related expression on The Village Idiom.
Practise it
Add it to your daily practice or see every verb with up.
Further reading: fall apart on Wiktionary (CC BY-SA).