Why Suction Cups Stick (It's Not Suction)

Tue, 15 Sep 2026 00:00:00 +0000

TL;DR: Nothing “sucks” a suction cup onto a wall. You live at the bottom of an ocean of air that pushes on every surface with about 10 newtons (roughly a kilogram of force) per square centimetre. Pressing a cup squeezes the air out from underneath; the rubber springs back and enlarges the cavity; the few molecules left inside now fill a bigger space, so the pressure in there drops (Boyle’s law). The atmosphere outside is still pushing at full strength, the inside is pushing back with much less, and that imbalance pins the cup to the surface. The holding force is just the pressure difference times the sealed area, F = ΔP × A. Peel an edge and air rushes in, the difference vanishes, and the cup falls. Same trick an octopus uses underwater. This is the first Lunch Break Physics: a weekly bite of everyday physics, Tuesdays at noon.

A quick note on where this comes from: this series was born at a reception at a broadcast conference in Amsterdam. Octopus was on the menu, and an octopus arm had stuck itself to someone’s plate so firmly that trying to pick up the arm lifted the plate along with it. That started a conversation about what “suction” actually is, and it turns out the honest answer is “not suction.” Everything below is standard physics; sources are at the bottom, and if I’ve oversimplified something, the comments are the point.

schristoph.online

Why Suction Cups Stick (It's Not Suction)