[ISL]

Think about how large the forces will be at the first tooth interface at the left (or in the rack). How strong does that tooth need to be?

Alternatively, you can use it the other way. Connect the gear at left to a tectonic plate. Rest your finger on the gear at right. Voila! You can exert a force great enough to stop the tectonic plate's motion. Plausible?

When Archimedes said, "Give me a lever long enough, and a place to stand, and I'll move the Earth.", he actually meant something more like, "Give me a lever long enough, and a place to stand, and I'll change the momentum of the Earth very very very slowly. Unless that lever is incredibly strong and I have access to a considerable source of energy."

[ultimoo]

"Alternatively, you can use it the other way. Connect the gear at left to a tectonic plate. Rest your finger on the gear at right. Voila! You can exert a force great enough to stop the tectonic plate's motion. Plausible?"

Nope, the question here would be whether the material used to construct the left gear withstand the force that a tectonic plate exerts given that the gear system will not allow it to move. I don't think the mechanics of the tectonic plate exerting force on our gear system and our gear system exerting force on the tectonic plate are symmetrical.

[lifeformed]

Good point. And even if the gears were made of unobtanium, the whole gearbox would have to be mounted on the opposite tectonic plate on top of breakable rocks.