The rate of change of momentum of material point is proportional to the net force of all the forces acting on it and in the direction of that force

It is THE NEWTON’S SECOND LAW, or in other worlds THE BASIC LAW OF NEWTON’S DYNAMICS. It is valid for forces of any physical nature.

Let us rewrite the Newton’s second law in a following form:

The production of force on a time of its action dt is called impulse of force. Then the basic law of dynamics can be formulated as:

The increment of momentum of material point equals
the elementary impulseof force, which exerts on it

If force is constant then, expression is simplified:

.

If the velocity of moving particle is very much less than that of light in vacuum then mass of particle is constant and the base dynamic law can be written as:

.

But, is acceleration of material point.

Therefore

or

It is the form of the Newton’s second law.

Acceleration of material point is directly proportional to the force acting on it,
inversely proportional to the mass of the particle, and coincides in direction with the force.

We can see that it is the special case of the second law of dynamics, when the mass is constant. From the last formula the physical sense of mass as the measures of inertness of body is followed. However the gravitation law includes mass too:

Here mass has quite another functions, it is measure of gravitation interaction

Numerically:

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