Turn the Crank
Read the puzzle
Five gears mesh in a row along the top; the first, big one at top left turns clockwise. The fifth carries a pulley joined by a crossed belt to a pulley on the bottom-right gear. Along the bottom, five gears mesh in a row; counting from the left, gears 1 to 4 each carry a rope drum and gear 5 is the belted one. Lantern A hangs from the left side of drum 1, B from the right side of drum 2, C from the right side of drum 3, D from the right side of drum 4. Which lantern goes up?
The big gear turns clockwise. Which lantern goes UP?
LANTERN C
Each mesh and the crossed belt flip the spin.
How to solve it
Work out each gear's direction along the chain: meshing gears turn opposite ways, and a crossed belt also reverses the direction.
Top row: big gear clockwise, second anticlockwise, third clockwise, fourth anticlockwise, fifth clockwise. The crossed belt flips that, so the bottom-right gear turns anticlockwise. Moving left along the bottom row: the D gear turns clockwise, the C gear anticlockwise, the B gear clockwise, and the A gear anticlockwise.
Now check which side each rope leaves its drum. On a clockwise drum the right side moves down and the left side up. On an anticlockwise drum the right side moves up and the left side down. A rope rises with the side it hangs from.
A hangs on the left of an anticlockwise drum: down. B hangs on the right of a clockwise drum: down. C hangs on the right of an anticlockwise drum: up. D hangs on the right of a clockwise drum: down. So lantern C rises.
The usual slip is treating the crossed belt like a plain belt, which keeps the direction and flips every result along the bottom. Another is ignoring which side of the drum the rope hangs from.
Learn the method: Gear Train Puzzles: Which Way Does the Last Gear Turn?
