A question on escape velocity

reply to post by CLPrime


I must have a different link. All the link in the OP says is;

Escape Velocity
the speed needed for an object to break away from the gravitational pull of a planet or moon

I don't understand how so much discussion centers around that.

reply to post by Illustronic


The sentence (literally labelled "Sentence") below that reads

After blastoff, the space shuttle has to go seven miles per second to reach the escape velocity of Earth.

And the picture caption says

NASA's New Horizons spacecraft is the fastest ever launched, speeding away from Earth at an escape velocity of 36,000 miles per hour. Image Credit: NASA

with 36,000 mph being the escape velocity of the Solar System.

I saw those as separate questions, but I agree that the information is brief and vague, I didn't follow back to get a feel for the context of that page.

I have found that pinpointing relative speeds on the internet is quite a chore. I read that the minimum speed to escape the solar pull from earth orbit is 36,900 mph, which I read New Horizons did. Now I see NASA stating 36,00 mph, is that proper rounding out? I believe the 'kid's learning center' usually take big subjects and dumbs them down for interest purposes. If the kids are interested enough they find they make discoveries brief descriptions smoothed over.

One can find that in any profession, the peers don't really want to tell you the whole story, unless they want to bombard you with too much information to sift through for a competitive advantage.

I don't know, thats how I see it.

I will agree that page has serious faults. To a level 101 student, maybe not so much, except I'm not sure I understand the context of achieving orbit and escape velocity in the stream. It didn't appear to be a continuous topic.

reply to post by Illustronic


I think I know what the "Sentence" part was getting at. It was, of course, just using the term in a sentence, and I don't think it was meant to indicate that the Shuttle actually has reach escape velocity. Perhaps a better way to word it would have been, "After blastoff, the space shuttle would have to go seven miles per second to reach the escape velocity of Earth."

Escape velocity is an instantaneous velocity. It's the required velocity that something has to start moving instantaneously at the surface of a planet to overcome the constant deceleration of gravity.

Originally posted by CLPrime
reply to post by Illustronic

 

The sentence (literally labelled "Sentence") below that reads

After blastoff, the space shuttle has to go seven miles per second to reach the escape velocity of Earth.

And the picture caption says

NASA's New Horizons spacecraft is the fastest ever launched, speeding away from Earth at an escape velocity of 36,000 miles per hour. Image Credit: NASA

with 36,000 mph being the escape velocity of the Solar System.

edit on 22-3-2012 by CLPrime because: (no reason given)

They are saying at an escape velocity. That's an indefinite article.

reply to post by WhatAreThey


The issue's not with the picture caption. I was just providing that because it's on the page. And the indefinite article in this case does not indicate any old escape velocity - rather, it indicates one specific escape velocity out of an innumerable amount. When you drive somewhere, you don't go at the speed of 55 mph, do you? Of course not...you go at a speed of 55 mph (or whatever you drive). In the same way, New Horizons travelled at a specific escape velocity, not the specific escape velocity (which would indicate that there is only one possible escape velocity).

Why am I arguing grammar on a physics question?

Also, in response to your previous reply: we know what escape velocity is, that's not the issue.

As far as the second question about black holes: Photons are moving with the instantaneous velocity of c. The space-time geometry warping past the event horizon is such that all paths lead toward the singularity and you are now infinity far from the event horizon, both physically and allegorically. It's an issue of the event horizon being relativistic and not Newtonian.

Originally posted by CLPrime
reply to post by Illustronic

 

Yet that's what this whole discussion has been about. A rocket doesn't need to achieve escape velocity because it experiences continuous thrust. The implication is that the rocket experienced an initial period of thrust at liftoff to propel it to escape velocity, and then it coasts into space. This certainly isn't the case.

The rocket is only used as an example of something that goes into space, it can't be used to illustrate escape velocity on any legitimate scientific basis.

Surprisingly, it seems you are the only one who understands my O.P. 100%.

It's been interesting to see how differently others interpret the question. Almost more so than the answer!

reply to post by OZtracized


I happen to quite literally be in the business of understanding what I read.