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Screwdrivers, golf balls, fuel efficiency: How I wasted my July 4 vacation

Screwdrivers, golf balls, fuel efficiency: How I wasted my July 4 vacation

We’re sitting around the shop on the Fourth of July watching it rain, so instead of rolling out assorted summer toys powered by internal combustion engines, a guy who shall remain nameless says, “Hey, watch this!” and picks up a compressed-air hose and a screwdriver.

I realize this starts off like a redneck joke—and I assure you no one was injured in the making of this blog—but bear with me. With the air nozzle in one hand and the screwdriver in the other, he begins to blast away. The screwdriver shakes a bit in his fingertips before he opens his hand and the tool just hangs in the air, suspended.

Apparently this is a common shop trick well known among mechanics, and I don’t think I’m revealing any guild secrets by discussing it—although it’s likely just another reason customers are not allowed past the sign that says “No unauthorized persons beyond this point! (All repairs: Labor $125 per hour.)”

Nonetheless, I thought it was a very cool trick. And being an inquisitive sort, stuck in a shop on a rainy holiday, I fetched the iPad.

Sure enough, YouTube has it covered. A representative video is here:

Here's a good explanation (and this guy makes me feel better about just wasting a rainy morning looking into floating screwdrivers. If you’re not into science enough to spend 7 minutes on the video, skip ahead):

The thing is, I’d never given much thought to dimples on golf balls. I knew they were there to help golf balls fly straight, but since they don’t seem to fly very straight when I hit them, my interest was limited. But his mentioning pickup truck aerodynamics got me to thinking—meaning, it got me googling.

Sure enough, on the physics page at StackEchange.com, someone asks the question: Why aren't airplanes like golf balls? (Except I’m thinking trucks, but we’re getting there.)

The short answer is illustrated at right, from Fundamentals of Aerodynamics.

Now, wouldn’t a typical car or truck be more the blunt body than a slender body? I must’ve been thinking out loud because an offspring, who’s having a hard time sufficiently demonstrating his absolute boredom with a rainy day away from a video game console, says “Myth Busters built a car like a golf ball once.”

Indeed they did, and guess what? They are dumfounded to discover their test runs with dimples on a car actually showed a significant improvement in fuel efficiency, about 11 percent:

 

Fastskinz patent illustration

Now I was getting interested and googled further, only to find that the patented dimpled car wrap fad had already come and gone, at least according to this post from Popular Mechanics:

But I’m not deterred, dismissing the auto wrap for a number of reasons. Then I find it, my proof that trucks that look like golf balls are coming: Wind tunnel tests show that dimples about 4 centimeters (1.6 inches) across on a full-size truck would cut drag the most—by about 28 percent!

Except, that’s based on a high school kid’s science fair project.

Not that she’s wrong, I say. But the sun came out and I had July 4 to tend to. Inquiries have been made of people who actually know what they’re talking about. We’ll see.

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