new descriptions of momentum and inertia

Why do objects with mass have momentum, and why is momentum conserved?

Why do objects have inertia, and why does inertia increase with greater mass?

Author Ngo Quang Ha has developed a new theory of spacetime to analyze the momentum and inertia of an object with mass.

The book (in English) is available on Amazon: https://www.amazon.com/dp/B0HCGYPFK1