Engineering

12 breaks

How things are built, and why they don't fall down.

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Why a falling pole can be held up: feedback, and the PID controller A pole on a cart wants to fall, and a controller that watches the lean and shoves the cart can hold it up. But how hard it pushes matters: too weak and it… Engineering4 min read Why a dam is fat at the bottom: water's push grows with depth squared, its tipping with depth cubed A dam is fat at the bottom and slim at the top because water pressure grows with depth, so the push grows with depth squared and the tipping effect with depth… Engineering5 min read Why bridges are made of triangles: a square folds, a triangle cannot A square made of four pinned rods folds flat at the slightest push, but a triangle of three rods cannot change shape at all. That one fact is why bridges… Engineering3 min read Why Taipei 101 hangs a 660-tonne ball in its upper floors: the tuned mass damper At the top of Taipei 101 a 660-tonne steel ball hangs in plain view. It is not decoration: it is a tuned mass damper that swings against the building and can… Engineering4 min read Why airliner windows have no corners: stress piles up at the tightest curve Cut a hole in a stretched plate and the force has to squeeze past it, so the metal beside the hole carries far more stress than the rest. For a round hole in a… Engineering5 min read Why steel beams are shaped like an I: the same steel, 25 times stiffer Put a beam across a gap and it sags: the top edge is squeezed, the bottom stretched, and the steel in the middle does almost nothing. That is why girders are… Engineering4 min read Why a stone arch stands without glue: Hooke's upside-down rope A stone arch has no glue, yet it stands for centuries because every block is only ever squeezed. In 1675 Robert Hooke hid the secret in an anagram: as a… Engineering5 min read Why a squeezed ruler bows sideways: Euler's buckling and the hollow tube Squeeze a ruler between your palms and it doesn't crush: it bows sideways and gives way. That's buckling, and it decides how slender a column can be. Euler… Engineering4 min read Why every bridge is made of triangles: a square frame folds, a triangle can't Push on the corner of a square frame and it folds flat. Push on a triangle made of the same sticks and nothing moves. The reason is simple: three side lengths… Engineering4 min read Why a 660-tonne steel ball swings to keep Taipei 101 still Skyscrapers sway in the wind, and gusts that match the tower's own rhythm can make it sway more and more. Taipei 101's answer is a 660-tonne steel pendulum… Engineering4 min read Hang a chain, flip it upside down, and you have the perfect arch In 1675 Robert Hooke hid a building secret in an anagram. Decoded after his death, it said: as hangs a flexible cable, so, inverted, stand the touching pieces… Engineering5 min read Why traffic jams appear out of nowhere Sometimes a motorway grinds to a halt and then clears up with no crash, roadworks or merge in sight. That's a phantom traffic jam, and it starts with one… Engineering4 min read