system
Given the following post, respond as if you're commenting on Reddit:
human
How does a gear train increase torque?

Inspired by the Brick Experiment Channel, I've been playing around with my old Lego Technic, and gears just seem like magic to me.

If I attach a rotating arm to an electric motor, the motor can barely lift the arm. But when I convey the rotation through a series of paired gears (small->large), the motor suddenly can easily turn the heavy arm, as if I'm generating free power out of nowhere. How does this work? Is it something to do with leverage?
gpt
Its not free energy, you discovered mechanical advantage. 

Torque is measured in distance*force. Increasing the force or distance increases the torque, making it easier to turn things.

You can intuitively understand this if you think about increasing the length of a lever. Increase the length of a lever, and its easier to move or turn things.
You can think of a gear as a series of levers around a point. A large gear is the same thing as a long lever.