The UK is currently experiencing a severe heatwave, with red alerts for extreme heat issued across more than 50 areas. Cars can become unbearably hot, but a simple hack using fluid dynamics can cool the interior faster than air conditioning.
The Hack: Open and Close the Door
Capital FM presenter Sian Welby shared the tip, originally from Professor Hannah Fry. She explained: “So you're in the driver's seat. You're going to wind down the window of the back left seat. Then you're going to get out of your driver's seat and just open and close the door [four times.] You get back in the car, it's cool.”
Science Behind the Technique
According to Professor Fry, the technique relies on fluid dynamics. “When you open and close the door quickly, the door sweeps out all the air in its way, creating an area of low pressure. That sets up bulk flow, drawing hot, sweaty air out of the car. The only way to refill it is with fresh air from the open window.” She noted that it takes only two or three goes to achieve a beautifully temperate interior.
Public Response
Viewers confirmed the technique works. One commented: “I used to do this without knowing the science behind it—it just seemed like the thing to do and it helps.” Another said: “Been doing this for 20 years with the blind belief that it's better than just opening all the windows. Thanks for the scientific pardon.” A third added: “This is a top tip, I've been doing this for years and can absolutely confirm it works as described.”
