'Flying' Plastic Bottle Pulled Behind Moving Truck With Aerodynamic Drag

A plastic bottle caught in a moving truck's aerodynamic drag appeared to 'fly.'
Brad Bergan

If littering were an insult to the environment, a recent video posted to Reddit of a 'flying' plastic bottle could be interpreted as nature's witty comeback.


Plastic bottle 'flying' behind truck from aerodynamic drag

A video shared on Reddit shows a plastic bottle caught in the lower-pressure aerodynamic drag of a truck driving down the highway. It's unknown whether this was a staged affair, or simply a happy accident that created a great case study of aerodynamic physics.

As the truck moves through the atmosphere of the Earth, it creates a low-pressure volume of space behind it — roughly shaped like a 3D teardrop — inside of which is less air pressure, which pulls the bottle in a perpetual spin behind the truck with an upward force equal to the force of gravity pulling it down.

Hence, it appears to 'float' mid-air.

via Gfycat

Aerodynamics of motion

Of course, things are more complicated. Wind speed and resistance, and the material of the bottle each play a role in holding the bottle in the air.

World-class runners sometimes run behind a car moving at the same pace, to take advantage of the aerodynamic drag, exerting less energy while maintaining a faster velocity.

Creating drafts is easy, but jumping out of trucks is ill-advised

Not that one needs a car to create a draft — anyone out for a run may experience this by looking for another runner keeping an ideal pace, and lining up behind them. The front-runner's draft, too, will feel like it's "pulling" the rear runner forward, as they maintain position within the aerodynamic drag.

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However, humans experience a lot more drag than a bottle because the latter doesn't have sagging clothes or body hair. It's super-smooth, extremely lightweight, and its rotation can act as an "air paddle" of sorts, pushing against higher-air-pressure areas to lift the rest of the bottle body upward.

A very lightweight body with a smooth surface is key for 'floating' behind a moving truck, so we can't stress enough how bad an idea it would be to leap out of the back of a moving vehicle in hopes of floating behind it.

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