I recently saw this tip from mathematician and presenter Hannah Fry who recently posted a video on social media demonstrating how to instantly cool the interior of your car.

The professor recommends rolling down one of the vehicle’s windows, and then rapidly opening and closing a door on the opposite side two or three times. 

There is a technical complicated reason for this which I will share at the end, but suffice to say it does work so if you are hot, hot, hot and about to get in your car do it now and don’t bother confusing yourself with the reason why it works.

So why does it work? It is all to do with fluid dynamics! What on earth is that I hear your cry! Well, I’ll tell you – fluid dynamics is the study of how liquids and gases move. Hannah Fry said:

“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 sweeps out all of the air that’s in its way, creating this area of low pressure that you get here. 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 air from over on the other side.”

Hannah Fry added:

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

This top tip should save you time in making your car’s cabin a lot cooler in the next heatwave!

Wendy Murray,
Editor, Our Town