Thermal Footpaths and Surfaces

The floor of a busy underground station handles about thirty thousand footsteps on a winter morning. Each one drives a few hundred newtons of force into whatever is beneath it. Below the tiles, at roughly sixty centimeters of depth, the soil sits at twelve degrees Celsius, unmoved by what the air above does – whether…

A stretch of motorway in southern Spain reaches 72 degrees Celsius at the surface on a clear July afternoon. The air above it sits at 38. Two meters below the asphalt, the ground holds steady at 17. That 55-degree differential exists for eight to ten hours, across every kilometer of that road, and not a…