Feather and Dime
acceleration due to gravity - freely falling bodies - air resistance
What it shows:
In the absence of air resistance all bodies, regardless of size or weight,
fall with the same acceleration at the same point above the Earth. Here
a feather and a dime (see Comments) fall under the influence of
gravity in an environment where there is no air to mess things up.
How it works:
The fall takes place within a sealed clear plexiglass tube 1.5m long and
5cm diameter (figure 1.). The valve at the base of the tube
screws into a vacuum pump platform to stand upright. Evacuate the tube
using the vacuum pump (which takes about a minute) and close the tube's
valve to isolate it. The tube can then be unscrewed from the platform
and tipped end-over-end by the lecturer.
figure 1. Plexiglass tube and platform
Setting it up:
Place the platform on a cart or the lecture bench with the vacuum pump
beside it. Leave both the tube and vacuum pump valves open. It is
good to show the fall with air in the tube first, showing the effect
of air resistance on the relative fall rates of the feather and dime.
Comments:
Instead of a feather, we use a folded piece of brightly colored tape, and
for the dime, we use a quarter. This is for visibility reasons, plus the
tape is less susceptible to static charge on the tube. The fall duration
is close even with the air, so it is a demo to repeat several times.
A video of the hammer and feather drop on the Moon by ( ? ) of Apollo (?)
would be good accompaniment, as would an account of Galileo's (supposed)
demonstration of dropping two canon balls from the top of the tower at
Pisa. Rating **