So David decided to craft an experiment to study this "slow-motion effect" in action. But to do that, he had to make people fear for their lives — without actually putting them in danger. His first attempt involved a field trip to Six Flags AstroWorld, an amusement park in Houston, Texas. He used his students as his subjects. "We went on all of the scariest roller coasters, and we brought all of our equipment and our stopwatches, and had a great time," David says. "But it turns out nothing there was scary enough to induce this fear for your life that appears to be required for the slow-motion effect."
But, after a little searching, David discovered something called SCAD diving. (SCAD stands for Suspended Catch Air Device.) It's like bungee jumping without the bungee. Imagine being dangled by a cable about 150 feet off the ground, facing up to the sky. Then, with a little metallic click, the cable is released and you plummet backward through the air, landing in a net (hopefully) about 3 seconds later.
Why A Brush With Death Triggers The Slow-Mo Effect : NPR