Demonstration of Force applied to objects allowed to move freely (with LEGO bricks)

This is a classic experiment demonstrating that, for each force component we apply, there is an equal and opposite force.
The demo is based on two Lego train carriages (freely moving objects) connected via a short string. A servo pulls the string showing that both carriages move.
The servo is controlled by an ESP 32 microcontroller which in turn connects to an iPad via BLE. This setup is also used in another video to control multiple LEGO (and LEGO compatible) trains.