Equations of Balance Tattoo

Today, a PhD professor of Materials Science came to get this eccentric tattoo.  In addition to being occupationally relevant, each of the three equations represents the initials one of his three children.

The first describes the conservation of linear momentum, the second is a variation of Gauss's Law (relating to electric flux), and the third is known as the "J-integral" and is used to predict the spreading of fractures in a material.