The feather-ball-drop experiment, on a grand scale

If you’ve made it to high school, you’ve probably at some point heard about Galileo’s discovery that objects fall at a rate independent of their mass.  (Turns out, this is only true if they’re very small compared to the Earth.  A marble, a piano, a blue whale are all negligible masses compared to Earth.  The Moon, however, is not, and it makes the Earth wobble quite a bit as it goes around the Sun, as the two bodies tug and pull at one another.)  Galileo understood that air resistance is a factor, but he’d also worked out that it’s actually the *only* factor that matters.  He tested this conjecture out by making spheres of equal dimensions but different masses and rolling them down an incline (which illustrates the effect just as well as dropping, but is easier for a man in sixteenth century Italy to measure accurately).  But what if he’d had access to a vacuum chamber?  This experiment has been done many times in vacuum chambers, but Brian Cox had the opportunity to try it out in the world’s largest vacuum chamber, at NASA’s Space Power Facility in Sandusky, OH.  And it is beautiful seeing it on this scale:

Of course, there is one even more impressive place that this experiment has been performed: the Moon.  What I like about this one is that it shows two things: first, that they are in vacuum, and second that they are in a much weaker gravity field than our own.  The hammer and feather fall at exactly the same rate, but slowly.

Now we just need to get a new moon mission so we can do this with better cameras.  😉

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