  We correct an error that occurs with certain frequency in popular literature
of Special Relativity, namely that supposedly that mass of moving objects
depends on the relative velocity of the object and the observer. In this
pedagogical paper, we explain that it is more correct to state that the linear
momentum and the kinetic energy increase with velocity, while the mass is in
fact an invariant, independent of the motion of the object and of the observer.
We give a few paradoxes that arise if one assumes a mass-dependent velocity.

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