A Behr free fall apparatus is seen in the video. The
bob is suspended at the top of the apparatus by an electromagnet. When the
current in the magnet is cutoff,
the bob falls to the ground. A spark timer triggering every sixtieth of a
second leaves a trail of spots on the paper tape behind the bob. In this
way, the distance vs. time data during the fall are obtained. This body,
although falling in a fluid would behave as if falling in a vacuum. See
section on
Experiment Analysis.