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.

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We did our measurement with the voice memo installed on iPhone 6. Either iPhone 7 or 8 has a same app that can be utilized. If you have iPhone 10 and you want to replicate our measurement, we recommend downloading an app such as Audio Memo since the default voice memo on iPhone 10 activates when you push the button, not when you pull your finger away. The voice recorder can be downloaded and utilized if you have an Android phone, with a caution when estimating latency error.
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The systematic uncertainties are estimated as variating the central value by adding the uncertainty. For instance, our average value for time is 0.44 s and its corresponding g is 9.36 m/s2. For device resolution, we add 0.005 s to the average and estimate g, which is 0.914 m/s2. We take the difference as the estimated uncertainty.
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