Two Texts, One Topic

Text 1: How a Canal Lock Works

A canal cannot run uphill. Where the land rises, engineers build a lock: a chamber with a gate at each end. A boat going uphill enters the lock through the lower gate. The gate closes behind it. Sluices in the upper gate are opened. Water flows in from the higher stretch of canal, and the boat rises with it. No pump is needed, because the water comes down by gravity. When the water inside matches the level above, the upper gate can be opened and the boat moves on. Going downhill, everything runs the other way: the water is let out, and the boat sinks with it.

Text 2: How a Windmill Grinds Flour

A windmill turns moving air into turning stone. The sails are set at a slight angle. Because of that angle, wind pushing on them cannot pass straight through, so it pushes them round instead. The sails turn a horizontal shaft. A large wooden gear on that shaft meshes with a smaller one on an upright shaft, which turns the millstones below. Because the smaller gear has fewer teeth, it spins faster than the sails do. Four turns of the sails can mean twenty turns of the stone. The grain falls between two stones. The top stone turns; the bottom one does not. The grain is crushed between them, and flour comes out at the edge.