2011: "Newton's Trajectories"

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nightbird
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2011: "Newton's Trajectories"

Postby nightbird » Mon Jun 25, 2018 4:40 pm UTC

Image

Title text: With just one extra line, he could have anticipated the 2003 film The Core, but some things are too audacious for even the greatest visionaries.

I can't believe I'm the first to post it. What's happening to these fora?
Last edited by gmalivuk on Mon Jun 25, 2018 4:49 pm UTC, edited 1 time in total.
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Re: 2011: "Newton's Trajectories"

Postby nightbird » Mon Jun 25, 2018 4:43 pm UTC

Anyway - it's been a while since an xkcd comic shook me as much, mainly because it tackles a thought I tend to have on a weekly basis. If there's one thing the remaining 21st century won't be, it's "boring". Anything else is in the cards.
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Re: 2011: "Newton's Trajectories"

Postby gmalivuk » Mon Jun 25, 2018 4:47 pm UTC

nightbird wrote:I can't believe I'm the first to post it. What's happening to these fora?

You were the first to post it, but you posted wrong.

(Also, it probably hadn't been posted already because the comic hadn't gone up yet.)
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Re: 2011: "Newton's Trajectories"

Postby rmsgrey » Mon Jun 25, 2018 5:23 pm UTC

gmalivuk wrote:
nightbird wrote:I can't believe I'm the first to post it. What's happening to these fora?

You were the first to post it, but you posted wrong.

(Also, it probably hadn't been posted already because the comic hadn't gone up yet.)


Explainxkcd had the page up at ~0400 (either UTC or UTC+1) more than 12 hours before this thread.

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Re: 2011: "Newton's Trajectories"

Postby qvxb » Mon Jun 25, 2018 5:25 pm UTC

It may not be either/or but both, as in the Star Trek episode "Mirror, Mirror".

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Re: 2011: "Newton's Trajectories"

Postby gmalivuk » Mon Jun 25, 2018 5:30 pm UTC

rmsgrey wrote:
gmalivuk wrote:
nightbird wrote:I can't believe I'm the first to post it. What's happening to these fora?

You were the first to post it, but you posted wrong.

(Also, it probably hadn't been posted already because the comic hadn't gone up yet.)


Explainxkcd had the page up at ~0400 (either UTC or UTC+1) more than 12 hours before this thread.

Then I guess the comic itself went up considerably earlier than they have been recently. (I no longer bother checking before that afternoon, since new ones are rarely up sooner.)
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Re: 2011: "Newton's Trajectories"

Postby Soupspoon » Mon Jun 25, 2018 6:43 pm UTC

The diagram is wrong, anyway. With an angled-up canon firing out, a freefall canonball will never enter a stable circular orbit like that. Even the others seem to inherit a side-wind or something.

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Re: 2011: "Newton's Trajectories"

Postby Old Bruce » Mon Jun 25, 2018 9:07 pm UTC

Soupspoon wrote:The diagram is wrong, anyway. With an angled-up canon firing out, a freefall canonball will never enter a stable circular orbit like that. Even the others seem to inherit a side-wind or something.

Perhaps the gun is on the equator and we are observing from above one of the poles? [genuine-puzzlement-face emoticon]

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Re: 2011: "Newton's Trajectories"

Postby speising » Mon Jun 25, 2018 10:17 pm UTC

Old Bruce wrote:
Soupspoon wrote:The diagram is wrong, anyway. With an angled-up canon firing out, a freefall canonball will never enter a stable circular orbit like that. Even the others seem to inherit a side-wind or something.

Perhaps the gun is on the equator and we are observing from above one of the poles? [genuine-puzzlement-face emoticon]

that doesn't help. every orbit with only one boost will always intersect the startig point. you need a second burn to circularize the elliptic orbit.

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Re: 2011: "Newton's Trajectories"

Postby Archgeek » Mon Jun 25, 2018 10:22 pm UTC

Old Bruce wrote:
Soupspoon wrote:The diagram is wrong, anyway. With an angled-up canon firing out, a freefall canonball will never enter a stable circular orbit like that. Even the others seem to inherit a side-wind or something.

Perhaps the gun is on the equator and we are observing from above one of the poles? [genuine-puzzlement-face emoticon]

I think it's only obliquely referencing Newton's cannonball, which was just a cannon firing straight ahead from a raised platform (which can hopefully be retracted 'lest it shoot itself in the event of a vacuum).
This diagram seems to feature a series of rockets lifting off from a proper launch pad, performing varying gravity turns. The first one just crashes, which does result in a fiery, toxic, carcinogenic mess weapons of sorts. The middle one seems to be an ICBM -- ending civilization in fire. The last is of course a simple but pretty sharp gravity turn into orbit.
speising wrote:that doesn't help. every orbit with only one boost will always intersect the startig point. you need a second burn to circularize the elliptic orbit.

If you look at Newton's old diagram, that cannon is pretty blatantly shooting itself. I think he either assumed a vacuum, or a very high platform.
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Re: 2011: "Newton's Trajectories"

Postby Heimhenge » Tue Jun 26, 2018 12:38 am UTC

Well here's the original from Principia:

Image

It's a horizontal cannon on a (to scale 1000 mile altitude and well above the atmosphere) mountaintop, so yeah, with the right projectile speed it's shooting itself. And yes, Newton must have been "assuming away friction" for this diagram to make any sense (at least for the longer trajectories).

What I'm wondering is why Randall didn't come up with a label for the shortest trajectory (D) ... maybe Evel Knievel's Snake River Canyon jump?

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Re: 2011: "Newton's Trajectories"

Postby da Doctah » Tue Jun 26, 2018 3:14 am UTC

Heimhenge wrote:What I'm wondering is why Randall didn't come up with a label for the shortest trajectory (D) ... maybe Evel Knievel's Snake River Canyon jump?

Or include the still-shorter trajectory in which the projectile is fired straight up and the cannoneer has to run to get out of the way before it comes down (and maybe even the Buster-Keatonesque outcome where Coriolis force makes dodging your own vertical fire unnecessary).

[Edit: really, spellcheck? You don't know the word "cannoneer"?]
Last edited by da Doctah on Tue Jun 26, 2018 4:45 am UTC, edited 1 time in total.

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Re: 2011: "Newton's Trajectories"

Postby Pfhorrest » Tue Jun 26, 2018 3:29 am UTC

da Doctah wrote:in which the projectile is fired straight up and the cannoneer has to run to get out of the way before it comes down (and maybe even the Buster-Keatonesque outcome where Coriolis force makes dodging your own vertical fire unnecessary).

And thus your attempts to dodge land you directly in the line of fire after all?
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Re: 2011: "Newton's Trajectories"

Postby Mikeski » Tue Jun 26, 2018 4:25 am UTC

Pfhorrest wrote:
da Doctah wrote:in which the projectile is fired straight up and the cannoneer has to run to get out of the way before it comes down (and maybe even the Buster-Keatonesque outcome where Coriolis force makes dodging your own vertical fire unnecessary).

And thus your attempts to dodge land you directly in the line of fire after all?

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