Posted: 1/7/2009 1:07:12 AM EDT
| Why is it that every time they talk about objects heading towards earth or traveling through space, they always seem to be traveling at approximately 30k to 35k miles per hour? Is that some kind of standard speed for matter that is hurtling through space? |
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Wild-assed guess: When studying parabolic/hyberbolic motion, a PARABOLIC orbit is a 'closed' orbit, meaning that it is a periodic (returning) orbit. A HYPERBOLIC orbit is no orbit at all, but a straight-line motion that has been perterbed by the Sun. in other words, something was passing through the solar system and its otherwise straight path was 'bumped' by the Sun.
WAG: 35K is probably right at the limit of where the para- and hyper-bolic orbits differentiate. |
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1) Space is a vaccum. There is no friction in space.
2) Objects in space are acted upon by their own gravitational field, as was as the gravity of other nearby objects. The mass of the object being acted upon, and the mass of the object(s) influencing it, will vary widely and result in fluctuating velocities. Further more, new objects are constantly being created in space through cosmic collisions and the explosion of stars. This explanation was brought to you by a Political Science major that took introduction to Astronomy several years ago and got an A-. Take it for what it is worth. 
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Quoted:
1) Space is a vaccum. There is no friction in space. 2) Objects in space are acted upon by their own gravitational field, as was as the gravity of other nearby objects. The mass of the object being acted upon, and the mass of the object(s) influencing it, will vary widely and result in fluctuating velocities. Further more, new objects are constantly being created in space through cosmic collisions and the explosion of stars. This explanation was brought to you by a Political Science major that took introduction to Astronomy several years ago and got an A-. Take it for what it is worth.  Leave it to a political science major to offer an explanation that completely dodges the question. |
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Quoted:
Quoted:
1) Space is a vaccum. There is no friction in space. 2) Objects in space are acted upon by their own gravitational field, as was as the gravity of other nearby objects. The mass of the object being acted upon, and the mass of the object(s) influencing it, will vary widely and result in fluctuating velocities. Further more, new objects are constantly being created in space through cosmic collisions and the explosion of stars. This explanation was brought to you by a Political Science major that took introduction to Astronomy several years ago and got an A-. Take it for what it is worth. Leave it to a political science major to offer an explanation that completely dodges the question. 
It's funny because it's true. It's like the presidential debates. Question is asked, and then they launch into a longwinded speech about something that has fuckall to do with the original question.
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Quoted:
Quoted:
1) Space is a vaccum. There is no friction in space. 2) Objects in space are acted upon by their own gravitational field, as was as the gravity of other nearby objects. The mass of the object being acted upon, and the mass of the object(s) influencing it, will vary widely and result in fluctuating velocities. Further more, new objects are constantly being created in space through cosmic collisions and the explosion of stars. This explanation was brought to you by a Political Science major that took introduction to Astronomy several years ago and got an A-. Take it for what it is worth. Leave it to a political science major to offer an explanation that completely dodges the question. 
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With regard to the OP, I don't know what you're talking about when you say that they always talk about objects traveling at that speed, but if you're talking about asteroids that are in the asteroid belt that dip down into an orbit that crosses the earth, those objects all start at about the same height from the sun, so, according to the laws of gravitation, they should all have about the same velocity when they get down to the height of earth's orbit (with minor fluctuations because the orbital elements of their orbits are all slightly different).
edited to remove my grumpiness now that I've had a cup of coffee.
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just to give you an idea of why the numbers are always so high.
Take the earths circum. and divide it by 24 and that is how many miles an hour the earth rotates. Earth about 24,900 / 24 = 1037 mph The moon moves a bit faster and the space shuttle is even faster. |
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That’s about 10 miles per second.
Earth’s escape velocity is about 7 miles per second… meaning anything that falls from space has to be going at least that fast when it hits us. Earth’s orbital speed is about 18-19 miles per second. Any object in our orbit will be going the same speed. An object in an elliptical orbit that crosses ours will be moving at a different speed of course. (A speed that will change based on it’s proximity to the sun.) So… it makes sense that an asteroid, in an elliptical orbit similar to ours might have a velocity within 2-4 miles per second of our orbital speed. Add in the escape velocity of Earth and I suppose 35,000 mph is a good guess about how fast something could be moving when it hits us. But an object could be far faster if it didn’t come from a near earth orbit but instead came from interstellar space. |
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The usual orbital speed for objects crossing Earth's orbit is between (roughly) 20 and 40 miles per second. 70,000 - 140,000 miles per hour would be reasonable figures.
30,000 mph is pretty damn low. Normal low Earth orbit speed is about 17,000 mph. That's what the Shuttle has to do to get into orbit. Comets and other stuff from the asteroid belt on out to the Ort cloud will be moving MUCH faster than that!! |
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Quoted:
With regard to the OP, I don't know what you're talking about when you say that they always talk about objects traveling at that speed, but if you're talking about asteroids that are in the asteroid belt that dip down into an orbit that crosses the earth, those objects all start at about the same height from the sun, so, according to the laws of gravitation, they should all have about the same velocity when they get down to the height of earth's orbit (with minor fluctuations because the orbital elements of their orbits are all slightly different). edited to remove my grumpiness now that I've had a cup of coffee. It doesn't even have to be objects that are hitting the Earth, seems the always refer to about the same speed when referring to manned probes heading to the outter reaches of the solar system. I guess my question is is why do you not hear speeds of 75k mph or 100k mph? Afterall, there does not seem to be anything to stop objects from attaining those speeds. |
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Quoted:
Quoted:
With regard to the OP, I don't know what you're talking about when you say that they always talk about objects traveling at that speed, but if you're talking about asteroids that are in the asteroid belt that dip down into an orbit that crosses the earth, those objects all start at about the same height from the sun, so, according to the laws of gravitation, they should all have about the same velocity when they get down to the height of earth's orbit (with minor fluctuations because the orbital elements of their orbits are all slightly different). edited to remove my grumpiness now that I've had a cup of coffee. It doesn't even have to be objects that are hitting the Earth, seems the always refer to about the same speed when referring to manned probes heading to the outter reaches of the solar system. I guess my question is is why do you not hear speeds of 75k mph or 100k mph? Afterall, there does not seem to be anything to stop objects from attaining those speeds. Simple orbital dynamics dictates the range of velocities that an object can be have and be in orbit around the sun (i.e., in our solar system). If an object exceeds that velocity, it's gonna escape the Sun's gravitational pull and be traveling in interstellar space. If an object is going too slow, it's gonna hit the Sun. Since the solar system has been around for billions of years, all those fast movers and slow movers were weeded out long before humans started looking at objects in the sky. Because the odds of getting hit by an object that's just floating in interstellar space are ridiculously small, the only objects you're gonna hear about are objects that are in our solar system and fall within the range of velocities that objects can have in our solar system. |
