How to quickly cool a hot car using just your arms and some fluid dynamics

Hannah Fry is a maths professor, science writer and broadcaster, and has reshared a – quite literally – cool tip on how to quickly lower the temperature inside your car using nothing more than a few embarrassing movements and a rear window.

No, she’s not advocating you go all Hitchcock and start spying on your neighbours to distract you from the raging hellscape outside, but instead she’s explaining how the power of air flow can quickly refresh your car’s cabin.

“There’s a fluid dynamics trick you can use to quickly cool your car down,” the good professor said in an Insta video. And she’d know, because she’s got a PHD in fluid dynamics.

First, she explains, you have to open the rear window on the opposite side of the driver’s door – handy if you’ve got four doors, admittedly not so handy if you’re in, say, a Lincoln Continental MkV coupe, but we digress – and then do the embarrassing thing.

“You do look like a bit of an idiot,” she said, “but just very quickly open and close the driver’s door.

“The reason why it works is that when you open and close the door, especially if you do it quickly, the door – as it’s moving outwards – it sweeps out all the air that’s in its way creating this area of low pressure.

“And then that sets up something called ‘bulk flow’, which is where all of the hot, sweaty, horrible air inside the car is drawn outwards. And the only way to refill it is with nice, fresh, easy air from over [the other] side.

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“It only takes about two or three goes and suddenly it’s beautifully temperate.”

Let’s be honest, you’ve done more embarrassing things in your car.

 

 

 

 

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A post shared by Hannah Fry (@fryrsquared)