Work Step by Step
Newtonian physics overlaps with quantum theory for objects composed of many slow-moving atoms, i.e., everyday moving objects as small as dust motes, bacteria, etc. Newtonian physics overlaps with relativity theory when objects are slow compared with the speed of light, and not too massive (the gravitational field should be relatively weak for Newtonian gravity to be valid). This still encompasses objects as large as the sun and planets. This is discussed on page 697.