You can use your phone as a magnetometer and measure the earth's local gravitational acceleration.

Just install this app and put your phone in your pocket, you can measure the local gravitational acceleration of the earth and other bodies in the solar system.

This app contains a pendulum (motor, weight, and scale) which you can use to measure the earth's local gravitational acceleration.

There is a magnetometer built into the phone. This sensor allows you to measure magnetic fields.

You can find experiments on this website that analyze your data, export it and let you further analyze it.