Simplify the following text for a Grade 8 native English-speaking person.
Original: In physics , the Navierâ `` Stokes equations , named after Claude-Louis Navier and George Gabriel Stokes , describe the motion of fluid substances .
Simplified: The Navierâ `` Stokes equations are mathematical equations that describe the motion of fluids . The equations are named after Claude-Louis Navier and George Gabriel Stokes .