The Principia logo depicts the legendary apple of Sir Isaac Newton. One story relates that Sir Isaac discovered gravity by an apple falling on his head. While this story is not historically accurate, it is a common myth - and would have undoubtedly caused problems with his coiffure. A more plausible story is that he sat under an apple tree and observed an apple hanging from the tree with the moon behind it in the distance. He then came to the realization that the earth's gravitational pull was acting on both the apple and the moon, which later led to the famous Universal Theory of Gravitation.

The motto on the logo is the general transport equation. This equation is also known as the general conservation law equation or the Navier-Stokes equation. The form shown in the logo is shorthand for

With appropriate substitutions this equation describes the conservation of mass, momentum, energy, moisture and turbulence.