The Dresden Files > DF Spoilers
(BG Spoilers) LTW Conservation of Speed w/ Mass Shift
BrainFireBob:
--- Quote from: Arjan on December 25, 2020, 03:08:54 PM ---Actually you can get mass from the nevernever as explained in skingame. You can temporarily store it there as well if I remember wok correctly.
--- End quote ---
Yes, but that mass should be created with potential, not kinetic, energy.
From a physics standpoint, the sparrow would slow down as its momentum and kinetic energy is shared with the new mass, which would then begin falling itself.
Of course, if LTW is smooth, he could time the change so that the elephant is nearly still from the extra mass, but so close that its new acceleration from gravity is still a considerable hit.
Or use extra magic to add matching velocity to the new mass as its added, that would also work.
Arjan:
Because the new mass comes with acceleration included.
vincentric:
Adding the mass changes acceleration but velocity is maintained. The only acceleration after the change is provided by gravity.
BrainFireBob:
--- Quote from: vincentric on December 31, 2020, 07:02:22 AM ---Adding the mass changes acceleration but velocity is maintained. The only acceleration after the change is provided by gravity.
--- End quote ---
Mass doesn't change acceleration at all. Momentum needs to be conserved, though, so unless the new mass is already accelerated to match, the same momentum is distributed over more mass, resulting in a slowdown.
EDIT: If you're interested, the relevant equation is the force of gravitation between two bodies.
F=m1a=G*( m1m2)/d^2
This means the acceleration due to the gravitational force is
a=G*m2/d^2
That's invariant from the frame of reference of m1.
Second edit: It's essentially a 100% nonelastic collision
vincentric:
I did assume the added mass came with matching velocity. It depends on how magic works :)
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