There are several apps you can use to measure g using a variety of sensors in smartphones. The simplest method is to simply drop your phone (onto something soft!) using the accelerometer will give you a readout of the acceleration. Note some apps add g so they measure 9.8 m/s^2 before they are moving.
Other methods involve timing how long a ball falls for over a known distance
There are a couple of nice methods using the free PhyPhox app and the acoustic stopwatch. Thanks to Kath Myers at Poole Grammar School who set this up as part of an IOP event.
The first method is to have a ball bearing on a ruler suspended over a biscuit tin or something hard. There is a known distance measured from the bottom of the ruler to the biscuit tin. Equations of motion can then be used to calculate the acceleration.
The trigger levels on phyphox are set to values that won’t trigger from background noise but will from tapping the ruler to release the ball. The ball bearing hitting the tin lid needs to be loud enough to stop the stopwatch
Another method is to again use the acoustic stopwatch but have a balloon that bursts and drops a mass onto a tin lid. Note that this must be quite heavy as the bursting balloon might cause it to fly outwards or upwards.
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