Question

What is the name of the mechanical process that breaks up food in the stomach?

Answer 1

Digestion

Explanation:

Food is mechanically digested through two ways in the stomach: Churning and Peristalsis.

Although Peristalsis most often occurs in the oesophagus, it happens in the stomach as well. Peristalsis is when smooth muscles contract in a rhythmic "wave-like" way to push food in one direction.

http://medical-dictionary.thefreedictionary.com/peristalsis
As Peristalsis occurs, the contraction and relaxation of the muscles cause the food to break up into smaller, more easily digestible bits.
https://en.wikipedia.org/wiki/Digestion

Churning occurs in the stomach, and is the stomach lining using the muscles it contains to physically squeeze the food and mix it with the digestive juices, working tandem with chemical digestion. This process takes place over several hours, until the food (now a creamy paste) enters the small intestine.
http://ib.bioninja.com.au/standard-level/topic-6-human-physiology/61-digestion-and-absorption/mechanical-digestion.html

I hope I helped!