Differing velocities in zero gravity?

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Marikurisato

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<p>I feel horrible for making my first post a question-begging thread, but I can't seem to word the question in a fashion that returns a relevant answer from search queries, so...<img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-embarassed.gif" border="0" alt="Embarassed" title="Embarassed" /></p><p>&nbsp;</p><p><font color="#0000ff">if a&nbsp; vehicle&nbsp; travelling at say 16,000 km/s in a straight line in space/zero g with no nearby planetary objects releases a smaller object from&nbsp; itself, what happens to the smaller object? Does it match speed given the original vessel's velocity and lack of atmosphere to cause drag? Does it lose velocity due to having no propulsion of it's own?</font></p><p>&nbsp;</p><p>Again, sorry if this post is in any way irritating or posted in ignorance of existed protocols, but this question has been bugging me for a month now. Thanks for reading!</p> <div class="Discussion_UserSignature"> <p>__________________- </p><p>"why?"</p> </div>
 
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Mee_n_Mac

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I feel horrible for making my first post a question-begging thread, but I can't seem to word the question in a fashion that returns a relevant answer from search queries, so...&nbsp;if a&nbsp; vehicle&nbsp; travelling at say 16,000 km/s in a straight line in space/zero g with no nearby planetary objects releases a smaller object from&nbsp; itself, what happens to the smaller object? Does it match speed given the original vessel's velocity and lack of atmosphere to cause drag? Does it lose velocity due to having no propulsion of it's own?&nbsp;Again, sorry if this post is in any way irritating or posted in ignorance of existed protocols, but this question has been bugging me for a month now. Thanks for reading! <br />Posted by <strong>Marikurisato</strong></DIV><br /><br />Sounds like a homework question.&nbsp; To be precise I'd want to know what's meant by the word "releases".&nbsp; For the moment let me assume the scenario is like a space shuttle coasting faaaaar out in space so there's neglible gravity from any planet or star or anything.&nbsp; The shuttle holds a small ball at the end of it's arm at some distance away. It then let's go without any pushing or pulling on the ball.&nbsp; So the thing to remember is that in this case good old Newtonian mechanics will give you a good answer; in particular F=MA or, re-arranging, A=F/M.&nbsp; So what forces are acting on the shuttle ?&nbsp; What forces are acting on the ball after it's release ?&nbsp; In general if there's no acceleration, what happens to velocity ? ...to position ??</p><p>FWIW there's the simple approximation and then there's a better one.&nbsp; For the better, truer answer remember Newton's Universal law of Gravitation; ie -&nbsp;gravity is a force (F) arising from what ?</p><p>If your question was a homework assignment I apologise for being obtuse but I think you can figure it out from here. If not, post back.</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> <p>-----------------------------------------------------</p><p><font color="#ff0000">Ask not what your Forum Software can do do on you,</font></p><p><font color="#ff0000">Ask it to, please for the love of all that's Holy, <strong>STOP</strong> !</font></p> </div>
 
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Marikurisato

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Sounds like a homework question.&nbsp; To be precise I'd want to know what's meant by the word "releases".&nbsp; For the moment let me assume the scenario is like a space shuttle coasting faaaaar out in space so there's neglible gravity from any planet or star or anything.&nbsp; The shuttle holds a small ball at the end of it's arm at some distance away. It then let's go without any pushing or pulling on the ball.&nbsp; So the thing to remember is that in this case good old Newtonian mechanics will give you a good answer; in particular F=MA or, re-arranging, A=F/M.&nbsp; So what forces are acting on the shuttle ?&nbsp; What forces are acting on the ball after it's release ?&nbsp; In general if there's no acceleration, what happens to velocity ? ...to position ??FWIW there's the simple approximation and then there's a better one.&nbsp; For the better, truer answer remember Newton's Universal law of Gravitation; ie -&nbsp;gravity is a force (F) arising from what ?If your question was a homework assignment I apologise for being obtuse but I think you can figure it out from here. If not, post back.&nbsp; <br /> Posted by mee_n_mac</DIV></p><p>&nbsp;I haven't been in college for ten years, actually, but I love the idea of the challenge. Having failed even remedial math I'll need to go study those equations, but I appreciate the hints! Thanks so much! </p><p>&nbsp;____</p><p>&nbsp;Ok, with some awesome hints from mee_n_mac&nbsp; I think the law that applies is "An object that is in motion will not change its velocity (accelerate) until a net force acts upon it." The article goes on to discuss that even in outer space there is friction or some net force acting upon it, which in this hypothesis let's assume is the pull of a star 18 billion kilometers away. Would the force of such a star have a noticeably effect though?</p><p>fun fun ponderings! </p><p>&nbsp;</p> <div class="Discussion_UserSignature"> <p>__________________- </p><p>"why?"</p> </div>
 
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Mee_n_Mac

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp;I think the law that applies is "An object that is in motion will not change its velocity (accelerate) until a net force acts upon it." The article goes on to discuss that even in outer space there is friction or some net force acting upon it, which in this hypothesis let's assume is the pull of a star 18 billion kilometers away. Would the force of such a star have a noticeably effect though?fun fun ponderings! &nbsp; <br />Posted by <strong>Marikurisato</strong></DIV><br /><br />My bad then, occasionally we do get kids looking to get their HW done.&nbsp; The "true" answer all depends on how closer to reality you want to come and the conditions you set on the question.&nbsp; With the conditions that you and the ball are waaaaaaay away from anything, comes the assumption that there's no gravity nor any gas nor any EM fields to interact with.&nbsp; So there you are coasting along at 16,000 km/s.&nbsp; You let go of the ball.&nbsp; There's no* forces acting on either you in the Shuttle nor the ball so there's no acceleration.&nbsp; With no acceleration your velocity (speed & direction) remain constant.&nbsp; Same for the ball.&nbsp; So you and the ball continue merrily along in the same direction at 16,000 km/s, just some distance apart from each other.</p><p>*But wait, both you (the Shuttle) and the ball have mass and so in reality will exert a gravitational force on each other. Slowly the ball will begin to move, ever accelerating, towards the Shuttle.&nbsp; And the Shuttle towards the ball as well, albeit sooo much slower.&nbsp; So in this deeper understanding of reality you both continue going where you were going at 16,000 km/s but also with the Shuttle & ball getting closer to each other until they run back into each other.</p><p>**Now in our reality you can't get faaaar away so as&nbsp;to be free from the Sun's gravity, at least not in our lifetime.&nbsp; Also there's solar wind, particles of "stuff", being blown of the Sun as well as other particles that are present in what we call a interstellar vacuum.&nbsp; So both you and the ball will be affected by the Sun's gravity (slowing, speeding, changing your and the ball's velocity)&nbsp;and by running into stuff (which will cause a drag force unless the solar wind and sunlight&nbsp;is giving you a push).&nbsp; Either you or the ball may get ionized, that is build up an electric charge. Now you have an electric field making&nbsp;another force, acting on you and the ball.&nbsp; And this is all without discussing the Pioneer Anomaly.&nbsp; So in a super duper approximation to real life ... it get's icky as to <strong><u>exactly</u></strong> what&nbsp;will happen.&nbsp;&nbsp; </p><p>But if I were asked I'd go with the * answer above as being close enough.</p><p>No doubt some more informed than I can give you a better rundown of all the forces involved in spaceflight.</p><p>&nbsp;</p> <div class="Discussion_UserSignature"> <p>-----------------------------------------------------</p><p><font color="#ff0000">Ask not what your Forum Software can do do on you,</font></p><p><font color="#ff0000">Ask it to, please for the love of all that's Holy, <strong>STOP</strong> !</font></p> </div>
 
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Marikurisato

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'> &nbsp;.No doubt some more informed than I can give you a better rundown of all the forces involved in spaceflight.&nbsp; <br /> Posted by mee_n_mac</DIV></p><p>not, it gives me a lot to ponder as it, and you are &nbsp;very awesome for that! Would that I could send you cookies through the internet ( no, not those kind) that was very helpful! Thanks!</p> <div class="Discussion_UserSignature"> <p>__________________- </p><p>"why?"</p> </div>
 
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DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>My bad then, occasionally we do get kids looking to get their HW done.&nbsp; The "true" answer all depends on how closer to reality you want to come and the conditions you set on the question.&nbsp; With the conditions that you and the ball are waaaaaaay away from anything, comes the assumption that there's no gravity nor any gas nor any EM fields to interact with.&nbsp; So there you are coasting along at 16,000 km/s.&nbsp; You let go of the ball.&nbsp; There's no* forces acting on either you in the Shuttle nor the ball so there's no acceleration.&nbsp; With no acceleration your velocity (speed & direction) remain constant.&nbsp; Same for the ball.&nbsp; So you and the ball continue merrily along in the same direction at 16,000 km/s, just some distance apart from each other.*But wait, both you (the Shuttle) and the ball have mass and so in reality will exert a gravitational force on each other. Slowly the ball will begin to move, ever accelerating, towards the Shuttle.&nbsp; And the Shuttle towards the ball as well, albeit sooo much slower.&nbsp; So in this deeper understanding of reality you both continue going where you were going at 16,000 km/s but also with the Shuttle & ball getting closer to each other until they run back into each other.**Now in our reality you can't get faaaar away so as&nbsp;to be free from the Sun's gravity, at least not in our lifetime.&nbsp; Also there's solar wind, particles of "stuff", being blown of the Sun as well as other particles that are present in what we call a interstellar vacuum.&nbsp; So both you and the ball will be affected by the Sun's gravity (slowing, speeding, changing your and the ball's velocity)&nbsp;and by running into stuff (which will cause a drag force unless the solar wind and sunlight&nbsp;is giving you a push).&nbsp; Either you or the ball may get ionized, that is build up an electric charge. Now you have an electric field making&nbsp;another force, acting on you and the ball.&nbsp; And this is all without discussing the Pioneer Anomaly.&nbsp; So in a super duper approximation to real life ... it get's icky as to exactly what&nbsp;will happen.&nbsp;&nbsp; But if I were asked I'd go with the * answer above as being close enough.No doubt some more informed than I can give you a better rundown of all the forces involved in spaceflight.&nbsp; <br />Posted by mee_n_mac</DIV></p><p>No need for discussiosn of the forces involved in spaceflight.</p><p>Your explanation is correct and captures the important physics, specifically that if the small body is released carefully without application of a force then it will simply continue to move along with the larger body.&nbsp; For problems such as this it is instructive to neglect the very small gravitational attraction between the two bodies, to better illustrate the domiinant physics.</p><p>If you do not neglect the graviational attraction between the two bodies then what you can do is consider the center of gravity of the two bodies, which if one is much more massive than the other will actually reside somewhere inside the larger body, and apply physics to concude that the center of mass is unaffected by the internal forces between the two bodies,&nbsp; It will travel in a straight line (in Newtonian mechanics) and the two bodies that determine it will either orbit one another or approach each other until they make contact and rejoin, held together by gravity.<br /></p> <div class="Discussion_UserSignature"> </div>
 
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