A Measurement of Gravitational Acceleration Using a Metal Ball, a Ruler, and a Smartphone

Abstract

These days, smartphones are popular commodities among students in high school and college. Students carry their devices all the time, so why not use such a popular electronic device to measure physical quantities such as g in physics labs? In this work, we report a “multiple tasking” method, a measurement technique that we came up with, for this very purpose. The method is simple: A person holds a ball using one hand and prepares to activate a recording function using another hand. Then the person drops the metal ball and starts the voice memo simultaneously. The time the ball takes to reach the floor is measured by reviewing the sound amplitude recorded, and the magnitude of g is calculated from the time. The error due to the auditory reaction time alone could be about 0.15 s, but we could measure the time in a 0.02-s range at 95% confidence level. A “using sound” technique to measure g was introduced before, but given that triggers such as a latch or something equivalent could introduce larger errors due to the device resolutions, we came up with our own.