The Fascinating Physics of a Floating Screwdriver

I’ve been posting a number of videos and links recently from the Applied Science channel on YouTube. People are going to start to think I have a #makercrush on Ben Krasnow. Guilty as charged. No one does a better job of explaining scientific principles and setting up fascinating experiments to test out scientific hypotheses than Ben. Watching his videos is like looking over the shoulder of a brilliant scientist-engineer at work in the lab; a scientist with an impressive ability to patiently and precisely explain what he’s doing as he’s doing it.

In this video, posted several years ago, Ben shows off the cool trick of floating a screwdriver in the air by hitting it with a stream of air from an air compressor. Neat trick. But how and why does it work? Ben gets to work (stand back, he’s going to use SCIENCE!) trying to figure out what the dynamics are here, in the airflow causing the tool to float, and in the structure of the screwdriver which allows this to happen.

The first thing that Ben does is create a dummy driver using a cylinder of plastic turned on the lathe for the handle and a piece of steel rod for the blade. Spoiler alert: It doesn’t float. But why? It’s so close to the shape, size, and weight of your average screwdriver. Ben does a drawing to explain the airflow dynamics at work around the two slightly different shapes.

Once he thinks he’s figured out the dynamics involved, he creates several new driver shapes to test out his hypothesis. He’s correct. Turns out, the shape of the butt-end of the driver is all that really matters here. Get the correct, rounded shape, and the flow dynamics around that end create a low-pressure zone towards the center of driver that pulls counter to the force of gravity and holds the driver in the air.

Ben even creates a fluid dynamics experiments box to try and visualize the flow around the different driver shapes. You can’t see the chaotic turbulence very well, but you can see the low-pressure stream created on the butt-ends of the drivers with the float-worthy shapes.

If this video whets your appetite for exploring flow and fluid dynamics in more detail, Ben also shows off the fluid demonstrator disc that he’s demo’d at Maker Faire. Plans for building one of these discs, and building it into a cool coffee table, can be found right here on Make:.