The relativistic four-vector version of this physical quantity is proposed under Lorentzian  translation, and Euler's first law relates this quantity with the velocity of a frame of reference.  Change in this quantity is called impulse, and its conservation leads directly to the law of  reciprocal actions and can be observed in Newton's cradle. According to Newton's second law,  force is the derivative of this quantity. For 10 points, identify this physical quantity, the product of mass and velocity of an object.
The relativistic four-vector version of this physical quantity is proposed under Lorentzian  translation, and Euler's first law relates this quantity with the velocity of a frame of reference.  Change in this quantity is called impulse, and its conservation leads directly to the law of  reciprocal actions and can be observed in Newton's cradle. According to Newton's second law,  force is the derivative of this quantity. For 10 points, identify this physical quantity, the product of mass and velocity of an object.
The relativistic four-vector version of this physical quantity is proposed under Lorentzian  translation, and Euler's first law relates this quantity with the velocity of a frame of reference.  
(linear) momentum [do not accept “angular momentum”]