Fun physics puzzle

A vibration-machine is a machine that vibrates through an electric
motor inside the machine. When it is turned on and someone is holding
onto the machine, the person can feel the vibrations of the machine.
But when it is turned off, the person cannot feel any vibrations when
holding onto the machine.

A balance scale is in equilibrium with one vibration-machine that is
turned off on each of the scale's two balancing pans, i.e., the two
vibration-machines weigh the same when each is turned off. Suddenly
while still on the balance scale, one of the machines is turned on
while the other machine remains off.

Question: Will the two machines still weigh the same according to the
balance scale? Why or why not?

Craig

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