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Independent researcher: Nguyễn Khánh Tùng
ORCID: 0009-0002-9877-4137
Email: traiphieu.com@gmail.com
Abstract
Every fundamental law of physics has a characteristic quantity and a unit of measurement (e.g., Newton for force, Joule for energy). The NKTg Law (Law of Varying Inertia) introduces a new physical quantity — varying inertia — defined by the interaction between position, velocity, and mass.
To measure this new quantity, I propose the NKTm unit, verified with NASA JPL Horizons data (Neptune, 2023–2024). Results indicate that NKTm is an independent fundamental unit, comparable in significance to Newton, Pascal, Joule, and Watt, with applications in astronomy, aerospace, and engineering.
This article clarifies the measurement unit of the NKTg Law (NKTm) and highlights its applications, many of which I have already implemented and shared as code examples on MATLAB Central.
1. Theoretical Basis
The NKTg Law describes motion under the combined effect of position (x), velocity (v), and mass (m):
NKTg=f(x,v,m)NKTg = f(x, v, m)NKTg=f(x,v,m)
Two expressions define varying inertia:
  • NKTg₁ = x·p (Position–Momentum interaction)
  • NKTg₂ = (dm/dt)·p (Mass-variation–Momentum interaction)
Both are measured by the same unit: NKTm.2. Dimensional Analysis
  • From NKTg₁: [ML2/T][M·L²/T][ML2/T]
  • From NKTg₂: [M2L/T2][M²·L/T²][M2L/T2]
Thus, NKTm is a unique unit that can take different dimensional forms depending on which component dominates.
For comparison:
QuantityUnitDimensionForceNewton (N)[M·L/T²]EnergyJoule (J)[M·L²/T²]PowerWatt (W)[M·L²/T³]Varying inertia (NKTg₁)NKTm[M·L²/T]Varying inertia (NKTg₂)NKTm[M²·L/T²]
3. Verification with NASA Data (Neptune, 2023–2024)
  • Position (x): 4.498×1094.498 \times 10^94.498×109 km
  • Velocity (v): 5.43 km/s
  • Mass (m): 1.0243×10261.0243 \times 10^{26}1.0243×1026 kg
  • Momentum (p = m·v): 5.564×10265.564 \times 10^{26}5.564×1026 kg·m/s
Results:
  • NKTg₁ = x·p ≈ 2.503 × 10³⁶ NKTm
  • NKTg₂ ≈ -1.113 × 10²² NKTm (assumed micro gas escape)
  • Total NKTg ≈ 2.501 × 10³⁶ NKTm
4. Applications
  • Astronomy: describe planetary mass variation, star/galaxy formation, and long-term orbital stability.
  • Aerospace: optimize rocket fuel usage, account for mass leakage, design ion/plasma engines.
  • Earth sciences: analyze GRACE-FO data, model ice melting, sea-level rise, and mass redistribution.
  • Engineering: variable-mass robotics, cargo systems, vibration analysis, fluid/particle simulations.
👉 Many of these applications are already available as MATLAB code examples that I have uploaded to MATLAB Central, showing how NKTm can be computed and applied in practice.5. Scientific Significance
  • Establishes a new fundamental unit (NKTm), independent of Newton and Joule.
  • Provides a theoretical framework for variable-mass dynamics, beyond Newton and Einstein.
  • Supports accurate computation and simulation of real-world systems with mass variation.
Conclusion
The introduction of the NKTm unit demonstrates that varying inertia is a measurable, independent physical quantity. Like Newton or Joule, NKTm lays the foundation for a new reference system in physics, with applications ranging from planetary mechanics to modern space technology.
This article not only clarifies the measurement standard of the NKTg Law, but also connects directly with practical MATLAB implementations for simulation and verification.
Discussion prompt:
What do you think about introducing a new physical unit like NKTm? Could it be integrated into MATLAB-based simulation frameworks for variable-mass systems?
You can refer to the following four related articles to gain a deeper understanding of the NKTg Law and its applications