Margen
The Eiffel Tower doesn't always measure the same. Its 7,300 tonnes of iron expand in the heat: on a midsummer day, the tip can rise some fifteen centimetres compared with a freezing January morning. Nothing breaks or comes loose; it's the simplest physics there is, the same that makes a jam-jar lid give way under the hot tap.
There's an even better detail. The sun doesn't heat the whole tower at once: the side facing the sun expands more than the side in shade, and that difference pushes the summit towards the cooler side. Over the course of a day, the tip traces a small curve across the sky, always leaning away from the sun like a sunflower in reverse. The shift can reach several centimetres.
Gustave Eiffel knew this and calculated it all before building it: his tower was designed to move. Perhaps that's why it has stood since 1889, while half the world believes iron things are rigid. The most famous of them all spends the summer stretching and dodging the sun.