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enter image description here

http://www.popsci.com/sites/popsci.com/files/styles/medium_1x_/public/import/2014/Hsu%20and%20Horanyi%20Graph%20AJP.png?itok=OSqMRad6

This graph shows the observed trajectory of lunar rover dust particles is roughly the same as in a simulated earth case. However, the earth has 6 times more gravity. Is this an accurate graph?

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    $\begingroup$ I don't understand your claim. The blue data on the graph clearly departs from the green curves . $\endgroup$ Jun 10, 2018 at 22:47
  • $\begingroup$ As Steve said, this seems to be a misinterpretation. The green curves are for particles of two different sizes in Earth gravity. Air drag is also a confounding factor - it slows the descent of the particles in Earth's atmosphere, allowing more time for the particle to be carried forward. $\endgroup$
    – kim holder
    Jun 11, 2018 at 0:03
  • $\begingroup$ Do you have a link to the entire paper? $\endgroup$
    – Hobbes
    Jun 11, 2018 at 8:13
  • $\begingroup$ Since the OP seems unwilling to provide a cite for the original paper, I found it here: aapt.scitation.org/doi/full/10.1119/1.3699957 Unfortunately it's paywalled and I don't have access. I speculate the OP got the picture here blackbag.gawker.com/… and is hoping for help debunking those debunkers. $\endgroup$ Jun 11, 2018 at 15:59
  • $\begingroup$ In any case. the connection between this paper and space exploration is as tenuous as the lunar atmosphere; the question can only be interpreted in light of Apollo Conspiracy Theory believers and I wish I had voted to close as off topic instead of unclear. $\endgroup$ Jun 11, 2018 at 16:09

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I think the OP has misunderstood what the graph shows. Each blue point is a separate piece of dust, and its position on the graph shows how high it got (up & down) and how far it travelled along the surface (left to right). Absent air resistance, this relationship doesn't depend on gravity. If I throw a rock so that it travels 10m up and 40m across on Earth, and then throw a rock at the same angle (but slower) so that it travels 10m up on the Moon, it will also travel 40m across (provided the distances are small enough that the curvature of the Moon is not relevant). It will take longer to do that on the Moon, but there is no time on the graph. At bottom left (short distances) the Earth and Moon curves line up, but further up or right, air resistance becomes a major concern on Earth which is why the black and green curves differ.

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  • $\begingroup$ This answer seems to articulate quite well something I vaguely suspected but couldn't quite pin down. $\endgroup$ Jun 11, 2018 at 6:50
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    $\begingroup$ This sentence bothers me "Absent air resistance, this relationship doesn't depend on gravity" because ballistic trajectories clearly depend on gravity. If a projectile is launched at 45 degrees at 10 m/s it will go a lot farther on the Moon than it will on Earth. The whole point of this paper seems to have been to back out the acceleration of gravity from the trajectories. $\endgroup$ Jun 11, 2018 at 16:07
  • $\begingroup$ @OrganicMarble: If a projectile is launched with the same force, yes. It will also go a lot higher, in direct proportion to how much farther it goes. The graph does not claim to show the results of launching identical projectiles with identical force. $\endgroup$ Jun 11, 2018 at 18:02
  • $\begingroup$ @NathanTuggy "Force" is not in play here,what matters is the velocity at launch. What do you think they used for the initial velocity of the Earth-bound particles for the simulation? If it wasn't the initial velocity they calculated for the lunar dust particles, what would be the point of the Earthbound curves? Surely you would hold the initial conditions equivalent to compare such curves, else the comparison is meaningless. $\endgroup$ Jun 11, 2018 at 18:05
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    $\begingroup$ If it doesn’t depend on gravity, what’s the distinction between the two outer (“lunar case simulation”) curves? $\endgroup$ Jun 12, 2018 at 3:27

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