*Reference: Fundamentals of Physics*

This law is post-Quantum Mechanics. Newton didn’t write this law, but he may just as well have written it if he were alive today.

**The Fourth Law: When a particle of matter is accelerated, its mass decreases. The decrease in mass is proportional to the increase in its speed.**

We have already established in **“Motion” in Quantum Mechanics** that the “absolute speed” of a particle is inversely proportional to its frequency. Therefore, as the speed of the particle increases from rest due to acceleration, its frequency decreases. This means, that the mass, or consistency, of the particles also decreases proportionally. When the acceleration goes back to zero and the particle returns to rest, its mass or consistency is also restored. The change in mass is so small in the inertial frames, that it is ignored.

The property that is fundamentally conserved is force. The force is conserved in the form of angular momentum as can be seen from the units of the Planck’s constant. The figure above provides a rough analysis that shows the proportionality of decrease in mass to increase in speed. The constant of proportionality, when fully worked out, shall include the Planck’s constant, and it would be extremely small.

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## Mass and Inertia

Let me also take this opportunity to define inertia in terms of mass.

**Inertia is the measure of consistency of substance per quantum. In case of matter, inertia is mass per unit particle.**

Therefore, Inertia may be compared on **The Spectrum of Substance** in terms of “consistency per quantum”, or “mass per particle”. Total Inertia shall be equivalent to total mass of an object. We may say that

**Upon acceleration, inertia converts to speed.**

This satisfies Faraday’s postulate of conservation of force.

Once we have a practical and simpler way of converting inertia into speed, and speed back into inertia, we shall have the INERTIAL DRIVE that has long been imagined in science fiction.

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