Free fall in vacuum: an educational Lab-experiment

I.A. Sianoudis^*,  M. Petraki, M. Serris, L. Prelorentzos

Physics laboratory, Department of Physics, Chemistry & Materials Technology,

Technological Educational Institution (TEI) of Athens,

Ag. Spyridonos, 12210 Egaleo, Greece, ^*) e-mail: jansian@teiath.gr

Abstract

Free fall experiments, based on various methods and technologies, can be found in every educational Physics laboratory. The proposed apparatus allows the study of the effect of air resistance in the movement of the falling body. The apparatus is relatively simple and easy to construct, and consists of a tube in which a ping pong ball is dropped. Various conditions of air pressure in the tube, measured with a sensor, can be realized through the use of an air-pump.  The motion of the ball is monitored via a series of LED-photo resistor gates which are placed along the tube, and which take measurements of the position of the ball at various points of its path. As the ball falls, it passes through successive photo resistor gates, the signals of which can be collected and analyzed with a common computer program.  Taking and analyzing data with the proposed  apparatus may be considered as an interesting and useful educational activity for first semester students. In this paper, we present a description of the apparatus, together with some experimental results exhibiting the role of air resistance in the motion of the ball. The experimental data presented were obtained during a typical student laboratory session.