[meteorite-list] Artificial Lunar Meteorites?

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Fri, 20 Mar 2009 02:09:35 -0500
Message-ID: <849B77FCC16B4BD8A78B7FB4E61BF22C_at_ATARIENGINE>

Eric Wichman wrote:

> I've got a few silly questions...
> Let's say you had a large canon powered by compressed air
> or some other high pressure gas.

Why not use a small rocket or a rail gun or a mass driver or...?
Doesn't matter to the problem how you launch it, OK?


> If you fired a projectile ( a moon rock ) from the surface
> of the moon toward Earth, would you be able to create
> enough force to reach escape velocity?

That's an engineering question. If you're a good enough
engineer, the answer is YES.


> Would the projectile continue to increase speed after leaving
> the barrel of the canon...?

Eric, go read a book by that nice Mr. Galileo or Mr. Newton.
Seriously. Get a simple old-fashioned physics text about dynamics
and the basic laws of motion and energy.

If you toss a rock, does it continue to speed up AFTER
it leaves your hand? If it did, then the experience of tossing
a rock would be that it goes further and further, faster
and faster, until it's so fast that it begins to glow with
frictional heat and blazes out the Earth's atmosphere like
a meteorite!

Funny. When I toss a rock, it just makes a little arc
and goes Plop! in my neighbor's yard.


> or does it stay at the velocity from which it leaves the barrel?

If you toss a rock straight up, does it continue at the same
constant 32mph that it had when it left your hand and climb
at a steady speed upward against the Earth's gravity, until it
leaves the Earth's atmosphere behind and enters space...
all at a stately 32mph?

When I toss a rock straight up, it slows down and down
until it can't go any higher, then falls back and hits me on
the head. In the interests of experimental science, I suggest
you get some good hefty rocks and try these tests. Space
travel would be so easy if your Laws of Motion were true.

OK, skip the tests.

You're on the Moon. You pick up a big rock and fit it
into your Super Duper Steam Powered Slingshot, capable
of firing a rock at 2380 meters per second, which oddly
enough is the Moon's excape velocity. (Actually you could
be a bit slower and still get to the Earth.)

The rock leaves the Super Duper Steam Powered Slingshot
at 2380 meters per second. After only one second of traveling
upward against the Moon's gravity, the rock is only traveling
at 2378.378 meters per second. That's because the Moon's
gravity is pulling back down on the rock with a force sufficient
to slow it down by 1.622 meters per second.

The Moon's gravity will continue to slow the rock at the rate
of 1.622 meters per second per second until, about 2 days later,
the rock is just barely crawling along at a snail's pace thousands
of miles above the Moon, when it reaches a place where the
strong gravity of the faraway Earth is pulling foward on the rock
just as strongly as the gravity of the much closer but weaker
Moon is pulling back on it, and the rock starts to fall toward
the Earth, now gaining speed instead of losing it.

Three days or so later, your mild-mannered rock will come
blazing into the Earth's atmosphere at a speed of almost 11,186
meters per second!

> Would the stones survive the trip through our atmosphere?

Here's where aim counts: the right angle of approach or perhaps
a grazing orbit or two before re-entry... Anything is possible
if you have sufficiently accurate control of your path. It's
do-able.


> If the projectile (moon rock) did survive all of this,
> would it be considered a meteorite?

That would depend on how the argument on this List came out...


> Scientifically speaking, wouldn't this be an interesting experiment?

Scientifically speaking, no... But, dude, it would be so much
kewler than a potato cannon or even a watermelon cannon!



Sterling K. Webb
Received on Fri 20 Mar 2009 03:09:35 AM PDT