Subject:
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Re: Falling thru earth revisited
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Newsgroups:
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lugnet.off-topic.geek
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Date:
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Wed, 8 Jun 2005 20:11:40 GMT
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Viewed:
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2698 times
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In lugnet.off-topic.geek, David Koudys wrote:
> Base model ignores the following--
> Rotation
> AIr Resistance
>
> [...]
>
> My idea is that basically the accelleration of an object going towards the
> center due to gravity and the decelleration of an object from the center to
> the other side basically cancels out, so we would just have to measure the
> distance/time from the entry point to the exit and figure in the thrust of
> the rocket across that distance and we'd have a pretty good idea of how fast
> it'l lbe going.
One other thing to think about is the amount of time something's been exposed to
something that increases its speed. For example:
Uncle Ben and Aunt Jemima have a race from point A to point B, and back to point
A. Aunt Jemima stays at a constant speed throughout the race. Uncle Ben starts
the race at *double* Aunt Jemima's speed, up until he reaches point B, at which
point he travels back to point A at *half* her speed.
At first thought, you'd think that they'd tie at the finish line, but really,
Jemima finishes in 4/5 of the time that Ben finishes. (He'd need to go 2/3 as
fast on the return loop in order to tie). Essentially, since he's going slower
for longer, it slows him down more than you might intuitively expect.
Not sure how that would affect the rocket model. But effectively, even if there
were NO gravity, the first half of the trip for the rocket would be moderately
slow compared to the final velocity, since the rocket (assumedly) doesn't run
out of fuel. Since we're ignoring air resistance, the rocket just keeps going
faster indefinitely, until it reaches the velocity at which it's spurting out
fuel (I think). Possible that it asymptotically approaches that velocity, I
dunno.
Anyway, how much time it spends being subjected to the negative forces of
gravity versus the positive forces may change whether or not the forces cancel
each other out. Being subjected to an equal force for *less* time means overall
that the *longer* duration force wins.
If the rocket's REALLY quick to gain momentum, chances are it's pretty much at
its max velocity right away, and the forces are close to balancing out. But the
slower it gains momentum, the less time it's going to be subjected to
detrimental accelleration on the other side of the planet since by the time it
gets there, it's going MUCH faster due to its own accelleration than when it was
going DOWN through the planet. So... it would actually help the rocket even MORE
if that's correct.
Hmm. Now I'm curious as to whether there's any merit to that idea or not.
Where's a good physicist when you need one?
DaveE
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Message has 1 Reply:
 | | Re: Falling thru earth revisited
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| (...) Yeah, like do you have to fly at an angle to avoid hitting the sides due to the earth's rotation? (...) Isn't this the whole idea behind the gravity slingshot they use to accelerate spacecraft? It worked in "2010" and I think NASA uses it all (...) (19 years ago, 22-Jun-05, to lugnet.off-topic.geek)
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Message is in Reply To:
| | Falling thru earth revisited
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| 'cause I've been ruminating about it.... So let's take this from the base model-- Base model ignores the following-- Rotation AIr Resistance you have the earth and a hole from where you are, going straight thru the center and right out to the other (...) (19 years ago, 8-Jun-05, to lugnet.off-topic.geek)
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