It's not mass, but equivalence principle states that its gravitational and inertial forms are equal, and an instrument measuring this quantity will show a value of zero in an inertial reference frame.
An equation named for this quantity is found by multiplying both sides of the Friedmann equation by the square of the scale factor, taking the derivative, and inserting the fluid equation, and this quantity also sometimes names the second of the Friedmann equations. The derivative of this quantity is multiplied by mu sub not times q squared over six pi c in the SI version of the Larmor formula, which gives the force of the (*) radiation reaction. It's not mass, but equivalence principle states that its gravitational and inertial forms are equal, and an instrument measuring this quantity will show a value of zero in an inertial reference frame. This quantity's time derivative is the jerk, and when it is multiplied by the mass it gives the force according to Newton's second law. For 10 points, give this quantity, which is the change in velocity over time.
An equation named for this quantity is found by multiplying both sides of the Friedmann equation by the square of the scale factor, taking the derivative, and inserting the fluid equation, and this quantity also sometimes names the second of the Friedmann equations.
acceleration [prompt on "a"]