Nick
you state:
Do you feel the tremendous force needed to swing it forward, relative to the slight force needed to swing it backward? Do you? No! You feel no difference in force from the bag even though you are propelling the bag forward at perhaps 2 M/sec and then backward at perhaps 0 M/sec relative to the airport floor, walls and building (while you are symetrically propelling the bag to plus and minus 1 meter per second relative to the conveyor belt, and relative to your arm and your body.)
However, if you were able to measure the forces required to swing the briefcase, you would indeed detect an increase in force to propel it at 2M/sec and a reduction in force to propel it 'backwards' at 0 M/sec due to the differecnce in air resistance (drag).
Now, move this argument to an L2 Puma suspended by a long rope on a crane moving along at 60kts. The Puma is pulled, like a pendulem, first in one direction, then the other, to the same angular deflection and then dropped from either end. Will it acheive 120kts G/S in one direction and 0 kts G/S in the other direction as it passes the vertical? Or will the air resistance, that's 'outside' the reference frame have any effect?
JJ