In this Engineering & Applications module, we want you to try out another experiment using your phone. First, watch the video. Afterwards, read the instructions below to do these experiments yourself!

The App

The app we use for the this experiment is one you can find on the app- and playstore, named “Physics Toolbox Magnetometer“.

To set up the app like in the video:

• Open up the app.
• In the top left corner, expand the menu. Then choose “Magnetometer“. This gives you the magnetic field the sensor in your phone is experiencing.
• Press the gear in the topright corner to open the settings. In the settings, under “Displayed Axis”, tick the “Show total”, and tick off the other axis buttons. This makes reading the x-y-z values easier.

You can find out where your sensor in your phone is by dragging a little magnet across the screen (NOT ON THE SCREEN!). Typically, the sensor is in the top left of the screen.

The experiment: Local gravity 2

This experiment is another way of finding your local gravity, one where you don’t have to drop your (fragile) phone.

• Take some rope (we used a fishing line) and stick a magnet to it (tape always works!).
• Use the rope and magnet as a pendulum, swooping the magnet across the sensor. You will see some peaks and troughs in the graph.
• To measure your local gravity, measure the time between a few of these peaks, and take the average.
• Also measure the length from the turning point to the center of the magnet, and note this.
• Finally, use the following formula: $g=\left(4{\mathrm{\pi ²}}^{}L\right)/{\mathrm{T²}}^{}$.

Of course, your found gravitational value might differ from the standard value. Can you explain why this deviates?