Torque vectoring is a relatively new technology that has been employed in automobile differentials, most commonly all-wheel-drive vehicles, that allows the amount of power sent to each wheel to be ...

So, if the driving gear has a diameter of 1 cm and the driven gear is 10 cm across, the gear train will increase the torque 10-fold while reducing the rotational speed by a factor of 10.

Guan-Chen Chen, Shao-Yu Wang, Design and analysis of hybrid stepping motors with integrated planetary gear trains, Science Progress (1933-), Vol. 104, Supplement 3: Conference Collection IMETI ...

When the train speed has increased sufficiently to match the engine speed, the fluid is drained out of the torque converter so that the engine is virtually coupled directly to the locomotive wheels.

Power transmission transfers mechanical power. Gear trains change speed/torque. Idler gears reverse rotation. Belts/pulleys and chains/sprockets transfer motion efficiently.