Mass
The basic SI unit of mass is the kilogram (kg). In physics, mass is not the same as weight, even though mass is often determined by measuring the object's weight using a spring scale, rather than balance scale comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity, but it would still have the same mass. This is because weight is a force, while mass is the property that (along with gravity) determines the strength of this force.
Mass point geometry
Solution. We may arbitrarily assign the mass of point formula_37 to be formula_38. By ratios of lengths, the masses at formula_39 and formula_40 must both be formula_41. By summing masses, the masses at formula_23 and formula_26 are both formula_44. Furthermore, the mass at formula_31 is formula_46, making the mass at formula_34 have to be formula_48 Therefore formula_35 formula_50 and formula_51. See diagram at right.