Big machines

How a wall of concrete across the Volta turns a falling river into electricity for Ghana and its neighbours, and how the spillway keeps floods safe.

How a pressurised water reactor splits uranium atoms to boil water, spin a turbine and light Cape Town, and how it is kept safe.

How a giant rotating machine chews through solid rock, carries the rubble away and lines the tunnel with concrete rings as it goes.

How a diesel engine as tall as a four-storey house turns a propeller nine metres across and pushes a container ship across the ocean.

How three long blades, a gearbox and a generator on top of a tower turn the steady winds of northern Kenya into electricity.

How a fan, curved vanes, a honeycomb and a narrowing duct make a smooth, fast wind, so engineers can watch and weigh the air flowing round a car, a wing or a ball.

How a steam locomotive turns coal and water into pulling power: fire, boiler, steam, pistons and rods, on the railway that runs from Mombasa to Kampala.

How a lift carries people up a Lagos tower: a car and a counterweight on steel ropes, a motor on the roof, and a safety brake that grips the rails if anything goes wrong.

How a lock lifts a boat from one river level to another with nothing but gates, sliding paddles and gravity.

How the legs of a 300-tonne jet catch it on the runway, stop it, steer it and fold away into its belly.

How a submarine sinks on purpose, flies through the deep on little wings, and comes back up again, with a boat of the South African Navy cut in half.

How a tower crane lifts tonnes of concrete high above a Lagos building site without tipping over, and how it climbs to grow with the building.

How a floating rig in a kilometre of sea drills a well three kilometres into the rock, and how heavy mud and a giant valve on the sea floor keep the oil and gas under control.

How one machine cuts the wheat, beats the grain out of the ears, blows away the chaff, and fills a trailer with clean grain while it drives across the field.

How limestone and clay are crushed, ground, burned at 1450 °C into clinker, then milled with gypsum into the grey powder that builds cities.

How a reverse-osmosis plant pushes seawater through membranes so fine that salt cannot follow, turning the Mediterranean into drinking water.

How one engine, a spinning rotor and two clever plates let a pilot lift straight up, hover, and fly any way they like.

How eight cylinders in a V, one crankshaft and four camshafts turn thousands of small explosions a minute into the smooth pull of a big car or pickup.

How a diesel engine, a pump and three oil-filled cylinders let one person dig rock and load a truck in seconds.

How a lamp, a giant glass lens and a slowly turning table send a coded flash far out to sea.