Physical Systems and Mass
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Chapter 5 examined the history of Newtonian mass and Ernst Mach’s critique of quantity of matter. Leaving aside the gravitational role of mass, the concept of mass carries two significant connotations: the quantity of matter and the inertial mass. Newton first conceived of matter as impenetrable places. He then dubbed the size of the impenetrable place as the quantity of matter, and took it to represent the amount of “stuff” there is in a body, in analogy to the volume that bodies occupy. Today such a conception seems outdated. First, particles such as electrons are structureless particles, and carry distinct mass parameters while only occupying a single point in spacetime. The notion of mass as an impenetrable region of space does not make sense if the mass parameter is assigned to a dimensionless object. Second, Mach’s critique of Newtonian mass had a lasting influence on interpretations of Newtonian physics. Mach’s overall strategy of emphasizing the inertial role of mass over its role as quantity of matter is widely accepted. The essential character of the concept of mass is said to be determined by Newton’s Second Law of Motion. According to this approach, mass relates the force impressed on the body to the acceleration it experiences.