Steve Mould Makes a Business Card Stick to the Ceiling With Vibration

Steve Mould sticks a coin-sized vibration motor to a business card, presses the card flat against a ceiling, and lets go. The card stays. A gap remains between the paper and the paint, thin enough that light barely slips through, wide enough that the two surfaces never meet. An eggshell does the same once a motor is fixed to it. So does a half-millimeter aluminum disc, once the motor gets loud enough to matter.

Bernoulli grippers have been used to pick up silicon wafers in chip manufacturing by forcing air via a nozzle, resulting in a quicker stream in a gap that presses less forcefully against the wall. As one might assume, Mold believed the claim would cover the fundamentals of the card, but up close, it comes apart. What’s going on here is that the gap we’re discussing is right in the thin-film range, when air acts more like a sticky sheet than a free-flowing stream, and viscosity does all of the heavy work. That’s why a rigid plate vibrating against that film is simply pushed away, much like an airless air hockey table floating a puck. A flexible plate is dragged in the opposite direction.

When you hang the card loosely, standing waves travel all over the place. Bring it close, and those standing waves turn into traveling waves that march straight across the gap. Each crest comes through, trapping a little pocket of air and squishing it toward the edge, similar to how a peristaltic pump squeezes down a tube in series. Air seeps out quicker than it can be pulled back in, lowering the pressure between the surfaces below that of the surrounding air, which simply pushes the card higher. Cut the motor, and the pocket refills, causing the card to fall. They tried a thin acrylic sheet first, which quickly failed; however, a stiffer plastic sheet hung in there a little better. The trick is that flex must be just enough to carry the wave without becoming too flexible that it fizzles out.

Scaling up to a level that could truly hold required two people: an engineer named Jamie and a 400 watt transducer, similar to what you’d use as a bass shaker in a home theater system. Mould’s ceiling is a little crooked, so they erected an artificial ceiling consisting of wood, nails, and a large anvil on top to add heft and keep the surface from shaking too much.

David Colasante, who has a patent for the thing under the name Orthosonic Lift, has even gone so far as to hang his own body weight from a garage rig using a thin aluminum wing and a few watts of exciters; he explained the importance of not wasting energy that should stay in the plate. Mould’s design was able to hold roughly 10-20 kilograms of dishes, a laptop, and a person on a rope before the grasp broke way, indicating a ballpark limit of a few dozen pounds based on the ceiling Mold built.
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