You fight with inertia all the time, and it usually wins. Sometimes it spills coffee into your lap while you take your car around a turn. Sometimes it throws you against a wall, for your own enjoyment, at a carnival. And sometimes the fight with inertia lets you defy gravity and take truly “hang ten”-worthy photos.
In the unattributed* photo above, two men pose for an opportunity to show off some awesome physics to the photographer (who hopefully wasn’t also the pilot). The man in front pours water into a cup like we on the ground would, except there is no ground beneath his feet. He pours out water directly up and towards the sky. How is such a photo possible?
As I said above, you fight with inertia all the time, and so you’re likely intuitively aware of how this photo is possible. Think back to the time when you were driving a bit too fast for an upcoming curve. Remember taking that curve and being pressed into the driver’s side door or gearshift. That was your crash course (ahem) in how inertia works. Before the curve both you and the car were travelling at some speed in the same direction. During the turn, your body was in motion and wanted to stay in motion. The car changes direction during but your body “wants” to keep going on in the direction it was before the turn. Being pressed up against the car door is the result of this directional discrepancy. You’re not being pressed into the door, per say, the door is getting in your body’s way.
Fighting inertia doesn’t have to be a nuisance or a carnival ride, it is a viable way to create space stations with artificial gravity, like in the recent sci-fi flick Elysium.
Back to the photo, another way to throw the first punch in the fight against inertia is to travel in a circle. Objects traveling in a circular path experience an acceleration inward towards the center of the circle and a force—the centripetal force—outward from the center. This means that the water from the bottle in the photo (assuming that the plane was doing some kind of aerobatic spin or barrel roll) would be pressed to the bottom of the plane during the maneuver. In fact, during the roll, the only way to pour out the water is towards the sky!
Of course, to pull this little physics stunt off, the plane must be traveling in a sustained circular path of some kind; a Top Gun-style maneuver would make a mess.
Water isn’t the only thing traveling outwards from the center of the spin in the photo, so is the men’s blood. At the moment that above photo was taken, artificial forces from the plane’s spin were pushing blood towards the men’s feet. It probably wasn’t a problem for them, but a more serious spin would make it a serious problem. Fighter pilots flying at ridiculous speeds have to wear special compression suits when they make sharp turns or curves, or else so much blood is marshaled into their feet that they pass out.
I don’t know how we would take a photo of someone’s blood being forced up towards the sky by aerial acrobatics, but I’d definitely like to see it.
Other than this photo being anonymously credited to some anonymous person on Facebook, I was unable to source the image. Anyone know?
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