Taking off weight is equivalent to applying a force equivalent to that of gravity and applying it in the opposite direction. It doesn't have to necessarily point to density.
If put that way (i.e. as a force based on an object's weight applied in the opposite direction), both momentum and kinetic energy can be cancelled. Impulse (Force applied over time) cancels momentum. That means a cancellation of velocity, which in turn causes kinetic energy to be reduced to zero.