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Relativistic kinematics relates positions, times, velocities, energy and momentum between inertial frames using special relativity. The Lorentz transformation changes the components while preserving the relevant Minkowski interval or Minkowski norm. It describes which motions and reactions are possible without by itself supplying the forces or reaction probability.

For a particle of rest mass $m$, its four-momentum gives $E^2-p^2{c}^2=m^2{c}^4$. At $v=0.6c$, the Lorentz factor is $1.25$, so $E=1.25m{c}^2$ and $p=0.75mc$. The relation remains the same in another inertial frame, although $E$ and $p$ separately change. Combining this invariant with conservation laws yields a reaction threshold.