Explanation: When you see a movie scene where a guy is clinging to the roof of a moving car, there's a good chance the stuntman in question is safely harnessed to the vehicle. Otherwise, it would be pretty much impossible to hang on for the ride.
Unless a car's windows are down, there's little to hold on to when you're on the roof. Even at speeds under 45 miles per hour, the MythBusters demonstrated that a person can't grip tightly enough to stay atop a car while it's moving. Any turning or stopping only makes matters worse, since Newton's laws of motion won't work in your favor. For example, if the car turns, an invisible nemesis called centrifugal force — a kind of inertia that keeps you flying away from the center of rotation — will literally shove you off the roof.
And when the driver slams on the brakes, your forward-moving body will keep right on sailing into the air. With the windows lowered — or if you hop on the car's slightly easier-to-grip hood — there's a better chance that you could hang on for dear life, but the odds still aren't in your favor.
Sorry, did we just ruin that summer blockbuster for you?