What happens when car's trunk pops open while driving? Yesterday my car's locking mechanism for the trunk malfunctioned and popped open while driving. Luckily I was cruising at very low speeds (around 15kph) and I just stopped and fastened it again.
What I'm wondering is what would happen if I were traveling at relatively high speeds, let's say at 100-120 kph. Would it open completely or just stay unlocked while keeping shut?
 A: Put simply, there is a pressure of air under the trunk. Consider the following crude diagrams:

The first is that of an average sedan. Now there is a certain effect known as the Coanda effect, which refers to the tendency of flowing fluids to follow the curvature of a surface, even when it deviates from its original flow direction. This is true generally when this deviation from the original flow direction is not very large, as in the sedan case. The flow is streamlined, and the air flows rapidly very close to the surface. I'm sure you must have seen the common physics classroom trick of blowing above a piece of paper(while holding it horizontally in air) causes the paper to lift. This can be mathematically expressed in the form of Bernoulli's equation. Here, The trunk of the sedan is like the paper. On blowing air rapidly above it, it will lift(fling open).
The second is a hatchback model. Depending on how rapidly the curvature of its surface changes, Coanda Effect is minimized in this case. This is because, rapidly flowing air, cannot follow the surface if it bends sharply. Notice how in the diagram, the flow is not strictly following the contour of the hatchback. This means that the air immediately outside is moving slower compared to a sedan, which also means greater pressure.  In other words, the chance of the trunk opening in this case is much less than that of a sedan. 
PS : This was my personal analysis of the question. Feel free to point out any mistake i made.
