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Ratio of projectile to ejecta mass, shoot the moon.

  1. Mar 7, 2012 #1
    Say we shoot the surface of the moon with various sized steel balls of size a cm and larger, say up to a km in size. Say the balls hit the surface of the moon moving at 20,000 mph. Is there a simple formula for the mass of the ejecta as a function of the mass of the projectile? Will the formula depend on whether the projectile hits dust or rock or a combination of the two?

    Thanks for any help!
  2. jcsd
  3. Mar 9, 2012 #2
  4. Mar 9, 2012 #3


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    Wow, nice find!
  5. Mar 11, 2012 #4
    Used the above calculator, seemed buggy for multiple calculations, and got the following result. For a steel projectile striking the moon at 10,000 mph perpendicularly, the mass of the projectile, M, was roughly proportional to the volume, V, of ejecta for sizes from 1 cm to 10 m,

    M ≈ V

    above that size

    M^α ≈ V

    Where α is less then 1.

    Is the above an example of scale invariance? If I draw a picture of the projectile next to the volume of ejecta I can change the scale but not have to redraw the picture, one picture works for a range of projectile masses and ejecta volume?
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