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Sci-Tech

Watch what happens when a spinning basketball gets thrown off a dam

More than 6 million YouTube viewers have already been mesmerized by the sight of a spinning basketball's crazy trajectory when tossed off the top of a giant dam.

Technically Incorrect offers a slightly twisted take on the tech that's taken over our lives.


Guess what happens next. Veritasium/YouTube; screenshot by Chris Matyszczyk/CNET

I'm not going to believe this until I see Stephen Curry do it.

However, when I saw that almost 7 million people have become fascinated (in just two days) by a YouTube video of a basketball being tossed off a dam, I had to investigate.

Posted by the scientifically inclined Veritasium, it shows the ball being thrown down the Gordon Dam in Tasmania. This is 415 feet high.

First, the curious types throw a ball down with no spin. The wind takes it a little bit, but it falls pretty much below the tossers.

Then they do it all again with the sort of backspin you might see on a three-point shot. It drifts off course like a a balloon on a windy day.


This is, the brains tell me, the Magnus Effect. I confess that the only time I've ever encountered a Magnus Effect is when a co-worker with body odor called Magnus walked into a meeting.

This one, however, is named after scientist Heinrich Gustav Magnus, who didn't like to be called Heinrich, preferring just Gustav.

His effect describes how the air affects all rotating balls as they fly through it. As the ball moves faster, the air on one side flows in the same direction as the spin.

However, air on the other side is going in the opposite direction. There is, therefore, a conflicting air-push that makes the ball deviate from what seems to be its obvious course.

In essence, it's the same thing as when you hit that horrible slice on your local golf course. You slap it with left-to-right spin (if you're a right-hander) and the Magnus Effect exaggerates that spin, until the ball goes through one of the upstairs windows belonging to an ugly house lining the fairway.

I suppose the only way you can prove this to yourself is to go to your nearest 415-foot dam and see if it works.

It's not going to be easy to get your ball back, though, is it? (If you do, however, you might schlep back up and go for a three-pointer.)

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