Eli5 How do things stay on my bumper when driving

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I recently drove approximately 15 miles of highway and back roads. Upon my arrival, while opening my rear van doors, I noticed one of those heavy copper staples laying on my bumper. This isn’t first time I’ve seen this. Phenomenon. What keeps items on the bumper? Thank you in advance

In: 3

Look up some videos of cars in wind tunnels. The air flowing over your car is mostly going straight back off the trunk. There is no wind going straight down from the trunk to blow it off the bumper.

At the rear of your car the airflow separates from your vehicle and becomes very chaotic, exactly how it looks depends on your car but a van will have a large area behind it where there’s basically a vacuum.

[Here’s a small diagram](https://imgur.com/aycarYG) I found where you can see what happens to the air velocity as it passes over your vehicle, the blue is zero (vacuum) while red is faster.

You can look up things like the drafting effect for real life examples of how the aerodynamics work.