Does a rail gun's ability to "hit a target 100 miles away in a perfectly straight line" prove that the Earth is "missing curvature"? No, that's not true: Such claims are "absurd" and "completely nuts," two physicists told Lead Stories. That's because rail guns fire projectiles that are subject to the same laws of gravity as all other objects on Earth. This means that their projection -- which is not in a "perfectly straight line" -- is inevitably pulled downward, causing it to "hit the ground at some point." The physics of a rail gun proves nothing about the curvature of the planet.
The claim originated in a post on Facebook on August 9, 2023, (archived here) that implied that the way a rail gun operates proves the Earth is "missing curvature." It read:
This is a rail gun.
it can hit a target 100 miles away
in a perfectly straight line.
That's 6,666 feet of missing curvature
#wheresthecurvature
Below is how the post appeared at the time of writing:
(Source: Facebook screenshot captured Thurs Aug 10 11:52:00 UTC 2023)
Named for two highly conductive rails with a projectile in between, a rail gun is a long-range weapon that forms an electromagnetic field to accelerate its projectile to launch, according to a 2008 article published in MIT Technology Review.
And like other weapons on Earth, the rail gun is also subject to the laws of gravity.
"This is an absurd claim, to begin with; one does not even need to necessarily bring in the curvature of Earth," Richard Lombardini, an associate professor of physics at St. Mary's University in Texas, told Lead Stories. In an email received on August 15, 2023, he wrote:
A rail gun shoots objects at around 4600 mi/hour [miles per hour] or 1.28 mi/s [miles per second]. It would take 78 seconds for it to travel 100 miles horizontally. We know that gravity accelerates objects downward at 32.2 ft/s^2 [foot per second squared], so the force is pulling downward on the rail gun projectile.
In other words, as the projectile is moving horizontally, it is also falling downward so that the trajectory is parabolic. For 78 seconds, the objection should fall around 100,000 ft. The statement that the projectile went straight for 100 miles is not considering the gravitational pull causing it to hit the ground at some point even if there were no curvature of Earth.
John Learned, a professor of physics at the University of Hawaii, Manoa campus, also told Lead Stories that the rail gun claim is "completely nuts."
"The rail gun shoots straight but the missile feels the pull of gravity too, and goes around the earth," Learned told Lead Stories in an email received on August 14, 2023.
Lead Stories has also debunked claims that NASA documents say that we live on a "flat, nonrotating earth," that a reflection in an astronaut's helmet visor from the Apollo 17 moon landing proves that it was a hoax and that airplanes fly "straight and level," proving that the Earth is flat.
