# Physical Phone Experiments

Phyphox is a freely available app that turns a smartphone into a mobile lab, so it has some great application for the physics classroom. Here are a few ideas – we hope you enjoy exploring it further!

Oscilloscope traces

When we teach sound, we traditionally look at oscilloscope traces for high/loud, high/quiet, low/loud and low/quiet notes. More often than not, this requires crowding a whole class around a tiny CRO screen and, of course, having the pleasure of getting that CRO to work as well.

Phyphox gives us a way of getting rid of the CRO and turning a demonstration into a genuine practical (as this is a sound experiment even the most basic smartphone or tablet will have a sound sensor). You will need two devices running Phyphox. Have one device running  ‘Audio Scope’ and the other running ‘Tone generator’, then place the two phones very close together so that the audio scope can ‘hear’ the note from the tone generator. Students can now change the frequency themselves (low or high) and change the amplitude by altering the volume on the device. They can see the traces on the audio scope. They could even do screenshots and save the traces.

Beats and speed of sound

You can also demonstrate the phenomenon of beats using two phones with this tone generator function. Set one phone at the default frequency of 440 Hz and another at a slightly different frequency (say 439 Hz). A periodic variation in volume can be heard with a frequency equal to the difference of the two source frequencies.

And you can even measure the speed of sound using two claps and two phones set on ‘Acoustic Stopwatch’ – just search for the YouTube video instructions!

Mechanics

Phyphox can also be used for lots of mechanics experiments. For example, measuring the acceleration due to gravity, g, by freefall, phone on a pendulum or a phone on a spring. And for an interesting exploration of centripetal force, the phone can be placed in a salad spinner (see below for instructions)!

Using Phyphox's remotely

Phyphox has a remote access feature, found in the Actions menu and accessed via the three vertical dots on each sensor’s screen). This feature gives you a URL which can be entered into a web browser to give remote control of the app and allows a teacher to display results to a whole class easily on a whiteboard.

For the purpose of the salad spinner experiment, it allows the user to start and end data recording. Select the Centripetal Acceleration function, place the phone in a salad spinner with a tea towel or something similar to give it some protection, start spinning at a range of rates and record the data on another device using the URL. The data output is two graphs: one of acceleration plotted against angular velocity and another of acceleration against angular velocity squared. Students could download the data and analyse it to confirm the relationship between acceleration and angular velocity, or take the experiment further and use the radius of the salad spinner to calculate the mass of the phone.

By IOP Coaches Mark Whalley and Neil Drury