Mass "M"
What it is
Mass is what a balance beam scale measures. ( A spring scale measures force.) Mass is the amount of material in a body involved in gravitational interactions, and a measure of a bodies resistance to change of motion. The concept of object is closely bound to the concept of mass.

Mass has become synonymous with energy although they are completely different properties. The energy of a body is proportional to its mass times a constant "C" squared times a gamma function. The gamma function, and therefore the energy of a body, is a function of its' relative velocity to other bodies in the universe. The confusion comes about because gamma is dimensionless. Note that mass and energy occupy different positions on the property charts, and consider that although the energy of a body may be different for different bodies in the universe, that the mass of a body looks the same to all other bodies.

The equation that defines the relationship between mass and energy
is:   energy = mass * C^2 * gamma
not: energy = mass * C^2


History
Isaac Newton (1642-1727) formulated the concept of mass to express his laws of universal gravitation.
The ancient Egyptians used balance beam scales as early as 5000 BC Although balance beam scales compare masses, the difference between weight and mass was not understood until Newton formulated his concept of mass.
Common equations
force = mass * acceleration
force = mass(A) * mass(B) * G / distance^2
energy = mass * C^2 * gamma
mass = (charge / length)^2 / length * permeability

Units
kilograms
grams
stone
hundredweight
pound
ounce
scruple
pennyweight
AMU's
Dalton
carat
grain
ton
slug

Editorial comments
I suggest that mass and energy are related by a tangent squared function, rather than by the gamma function mentioned above. The gamma function defines the relationship between mass and energy more precisely if one operates under the concept that one body is fixed in media (Time and space) and a second body is varying in media, but the tangent squared function is correct if one operates under the concept that interactions are symmetrical, and that two bodies interact about a common point (The system center of mass.) in a common time (The system period.).
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