Invert the evacuated tube
containing a coin and a feather to show that the two objects
fall at the same rate in the absence of air resistance.
Open the valve to admit air, then invert the tube to show that
the coin reaches the bottom first.
NOTES
The feather can get stuck
on the pointed electrode (used for a different demonstration)
or get sucked into the pump, so try to keep it away from the
ends of the tube prior to doing the demonstration.
