Now that’s dedication to science
Being a scientist takes dedication — there’s no doubt about it. But, for Norwegian scientist Andreas Wahl, dedication means risking his life. He first became known for jumping off the side of a building to demonstrate Newton’s Law of circular motion, but he has now taken his death defying stunts to a new level by having someone shoot at him with a gun underwater.
As a scientist, he was certain that he’d be safe. But, the expression of relief on his face showed that as a human, it was still a pretty terrifying experience. I feel that this is the right time to mention this: DON'T try this at home!
Now let’s get down to the real question: How is it that Wahl isn’t dead? For that, he has water resistance to thank. A substance’s density — the distance between its molecules — is what affects how fast something travels through it. If you’ve ever tried to run in water, you’ve experienced this effect. It requires much more effort to run in water than it does to run on land because water molecules are closer together than those in air. Running in molasses or something with even higher density would be even more difficult. Running in oil, on the other hand, would be easier than in water, but still harder than on land since oil’s density falls between the two.
Since Wahl’s team filmed the experience in slow motion, you can see that the bullet slows down as it slices through the water and eventually ends up on the pool floor before it gets anywhere near Wahl.
What about those bubbles? Where do they come from? According to an Outrageous Acts of Science video, even though the bullet doesn’t make it very far, it is travelling incredibly quickly as it exits the gun. This results in an area of high pressure in front of the bullet and an area of low pressure — a partial vacuum — behind it. In a vacuum, water boils, and as it evaporates, it creates the gas bubbles. The water around the gas then pushes in and increases the pressure, reversing the phase change.
“Yes!” he cries as he comes to the surface of the pool holding his precious bullet. Yes, science, it works!