what is meantby "Principle of the mass"?

Answer 1

The Principle of Mass is Newton second Law:

Acceleration that a free body acquires, under the action of a force results directly proportional to the mode (magnitude) of the force and of it same direction and sense.

This implies that the cocient between the magnitude of the force and the one of the acceleration is a constant, we can say then:

F / a = k

Constant K of proportionality depende on the property of the bodies and is designed with the name of mass, and of the units that measure the force and the acceleration. If F and a are measured in convenient units, constant k dependes exclusively on the mass, in which case we can say:

F/a = m

So, the magnitude of the force and the magnitude of the acceleration allow us to calculate the mass of a body. From here, when the force is equal but the acceleration is minus, its because the mass is more!. Yes, this looks a little abstract, but can be easily taken to our daily life.

For example, you can lift easily a toy car, but you can't easily move a real car!.

Answer 2

the mass of a body is constant throughtout the universe....
only the weight of a body changes because the different planets have diffrent gravitational field.....