Why gravitational forces are neglected when computing the force between charged objects?

Answer 1

A true scale uses known masses to balance out the forces. Think of the simplest system as a see saw type device. With nothing on it, the arm is level. Put the object to be measured on one side, and start putting known masses on the other till it is level. So the force down on the unknown object is m*g. Then on the other side you have (known masses)*g. Same force means the system is in equilibrium. Move to the Moon, and you still have the same forces on both sides. More sophisticate balance scales use leverage, so that the force from known masses is multiplied by the known arm length. Commonly seen in a scale at the doctor's office, where they move the weights back and forth, until it balances.

Answer 2

Gravitational forces are much weaker than electromagnetic forces for charged objects, so they can be neglected in most situations involving the force between charged objects. When dealing with charged objects, the electric force dominates because the electromagnetic interaction is orders of magnitude stronger than the gravitational interaction. Therefore, gravitational forces typically do not have a significant impact on the calculations of forces between charged objects.

Answer 3

That means that the objects considered have a small mass (probably a few tons, at most), and therefore, the gravitational attraction between them is insignificant.