# @stem_antics on Instagram

- **Type:** Video
- **Original URL:** https://www.instagram.com/p/Dd_utBJgsTh
- **Gondola URL:** https://gondola.cc/posts/71131432-stem-antics-instagram
- **Thumbnail:** https://img.gondola.cc/tr:w-,h-,fo-auto/postThumbnails/cdacbd1bee.jpg
- **Posted:** 2026-10-02T14:46:03.000+00:00
- **Account Owner:** Stem Antics (@stem_antics) — https://gondola.cc/stem_antics

## Caption

Sticking a business card to a ceiling needs no glue, no magnet and no vacuum pump. A small vibration motor and a thin layer of air are enough.

Bolt a coin-cell eccentric rotating mass (ERM) motor to a card, hold it a fraction of a millimetre beneath a flat ceiling, and it stays there. The card is not held up by force pressing against the ceiling. It is pulled up by the air in the gap.

The mechanism is squeeze-film flow:

- The motor drives the card up and down by tens of micrometres at roughly 100 to 250 Hz.
- On each closing stroke, air is forced radially out of the narrowing gap. On each opening stroke, it is drawn back in.
- Because the gap is thin compared with the card’s width, the radial velocity is large. Bernoulli’s principle says fast-moving air has low static pressure.
- Dynamic pressure scales as one half of rho times v squared. It is always positive, whichever way the air flows. So the pressure deficit in the gap does not cancel over a cycle. It averages to a net suction.

The required suction is modest. A standard 85 x 55 mm card has about 4,700 square millimetres of area. Supporting a card plus a 2 to 3 g motor needs a mean pressure deficit of only a few pascals. Atmospheric pressure is roughly 101,000 Pa.

Whether the film attracts or repels depends on the squeeze Reynolds number, which compares air inertia with viscosity. In a very thin, viscous, compressible film, gas is trapped and compressed. That gives net repulsion. This is the principle behind near-field acoustic levitation, described by E.O.J. Salbu in 1964 for squeeze-film bearings. In a thicker gap at a higher Reynolds number, inertia dominates, and the Bernoulli suction wins.

The ceiling trick works because the gap settles at the height where suction balances weight. Too close and the film pushes back. Too far and the suction fades.

A business card on a ceiling is fluid dynamics hiding in plain sight.

#stemantics #fluiddynamics #physics #engineering #stemeducation

## Stats

- **Views:** 15,848
- **Likes:** 212
- **Shares:** 0
- **Comments:** 5

## Tags

engineering, fluiddynamics, stemeducation, physics, stemantics

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