Snowshoa

Meet Snowshoa, a hiker standing on deep snow without sinking in.

Pressure is force divided by the area it acts on, p = F/A. The same force spread over a bigger area gives a smaller pressure. Snow can only hold a certain pressure before it collapses, so what matters is not just how heavy you are, but how widely your weight is spread. The SI unit, the pascal, is one newton per square metre.

A 700 N hiker on boots with 0.035 m² of sole presses on the snow with p = 700 / 0.035 = 20,000 Pa, or 20 kPa. On snowshoes with 0.2 m² it is 700 / 0.2 = 3,500 Pa, only 3.5 kPa, so the snow holds.

The same idea explains wide tyres on tractors, and why sharp knives cut: a thin edge concentrates force onto a tiny area, giving enormous pressure. Drawing pins have a broad head for your thumb and a sharp point for the board.

This is the average pressure; real pressure under a foot is uneven. Whether snow holds also depends on how compact and wet it is, not on a single number.