text: Alexander Kashlinsky used the term "dark flow" to describe an unexplained for of this quantity in galaxy clusters.
full_question: Alexander Kashlinsky used the term "dark flow" to describe an unexplained for of this quantity in galaxy clusters. The statistical dispersion of this quantity for an elliptical galaxy is related to its luminosity by the Faber-Jackson relation. This quantity's value relative to a rest frame is called the "peculiar type of it, and it is not explained by (*) Hubble's Law. The change in this quantity is related to the logarithm of the initial mass divided by the final mass by the rocket equation. By setting the kinetic energy equal tot he potential energy, one can derive the minimum value for this quantity for an object to escape from a body's gravitational field. For 10 points, name this quantity, the time derivative of position.
first_sentence: Alexander Kashlinsky used the term "dark flow" to describe an unexplained for of this quantity in galaxy clusters.
raw_answer: velocity [or motion; or speed] 