From Terry.Moffat at rongotai.school.nz Sun Apr 6 16:21:38 2008 From: Terry.Moffat at rongotai.school.nz (Terry Moffat) Date: Mon, 07 Apr 2008 08:21:38 +1200 Subject: eliptical orbits Message-ID: <47F9D991.DFDA.0008.0@rongotai.school.nz> Hi, can someone give me a simple reason why planets move in eliptical orbits. does it have something to do with the fact that the system is moving through space? ta Terry From bevans at es.co.nz Sun Apr 6 22:47:42 2008 From: bevans at es.co.nz (Bob Evans) Date: Mon, 07 Apr 2008 14:47:42 +1200 Subject: eliptical orbits In-Reply-To: <47F9D991.DFDA.0008.0@rongotai.school.nz> Message-ID: <5.1.1.6.0.20080407144440.02263c38@pop.ihug.co.nz> At 08:21 a.m. 7/04/2008 +1200, Terry wrote: >can someone give me a simple reason why planets move in eliptical orbits. It's just easier for something to get into an elliptical orbit than a circular one. A circular orbit requires the body to have just the right speed at just the right angle at just the right height/distance. >does it have something to do with the fact that the system is moving >through space? That's a negative. Bob Evans R W Evans, 15 Taiepa Rd, Otatara RD 9, Invercargill 9879, New Zealand Phone +64 3 2130329 Fax +64 3 2130327 bevans at es.co.nz http://homepages.ihug.co.nz/~Sbevans/home.htm From robcampbell at actrix.co.nz Mon Apr 7 06:34:21 2008 From: robcampbell at actrix.co.nz (Rob Campbell) Date: Mon, 7 Apr 2008 22:34:21 +1200 Subject: eliptical orbits In-Reply-To: <47F9D991.DFDA.0008.0@rongotai.school.nz> References: <47F9D991.DFDA.0008.0@rongotai.school.nz> Message-ID: <000001c8989a$f1241b40$0301010a@robert972970e8> Hi! Newton's explanation remains the simplest one that fully explains this, but I won't attempt maths in a text-only email! So, here's the hand-waving version. Earth satellites like the Moon or the ISS 'fall' toward Earth. They never arrive because there's a sideways component to their velocity. If the ISS really does move toward Earth, it loses PE and gains sideways KE. The sideways motion tends to draw it tangentially away from Earth - which doesn't prevent it coming closer (it does.) As it approaches Earth, tangential velocity builds up, slowing then reversing the Space Station's fall. It starts to rise, gaining PE as it does so, and losing KE. At its furthest point from Earth, its orbital velocity is lowest; at the nearest point, its orbital velocity is highest. This generates an ellipse, though at 10pm I can't illustrate this in words! A moment's thought will show that an ellipse is reasonable; 1/2 hour's thought with pen and paper will prove it. There's no difference in principle between a satellite orbiting Earth and a planet orbiting the Sun - just one of scale. Planets tend to follow elliptical orbits approximating to circles, maybe on account of their fiery origins. An ellipse is a squashed circle (apologies, mathematicians) with a major and minor axis rather than a constant radius. Really, a circle is the special case ellipse where the two axes are equal. Hope that helps, Rob Campbell -----Original Message----- From: phys-teach-talk-bounces at nzip.org.nz [mailto:phys-teach-talk-bounces at nzip.org.nz] On Behalf Of Terry Moffat Sent: Monday, 7 April 2008 8:22 a.m. To: phys-teach-talk at nzip.org.nz Subject: eliptical orbits Hi, can someone give me a simple reason why planets move in eliptical orbits. does it have something to do with the fact that the system is moving through space? ta Terry _______________________________________________ Phys-teach-talk mailing list Phys-teach-talk at nzip.org.nz http://nzip.org.nz/mailman/listinfo/phys-teach-talk_nzip.org.nz From phil.butler at canterbury.ac.nz Mon Apr 7 17:42:30 2008 From: phil.butler at canterbury.ac.nz (Phil Butler) Date: Tue, 08 Apr 2008 09:42:30 +1200 Subject: eliptical orbits In-Reply-To: <000001c8989a$f1241b40$0301010a@robert972970e8> References: <47F9D991.DFDA.0008.0@rongotai.school.nz> <000001c8989a$f1241b40$0301010a@robert972970e8> Message-ID: <468DDDC0BAEBD648821F71AF87A0284B07737BF6@cantwe2.canterbury.ac.nz> Hi all One of the nicest hand waving explanations is Newton's own figure which I have attached. I seem to recall that this email list doesn't take diagrams so it may be stripped off :-( The essence is to imagine standing on a tall hill (or the Auckland Sky Tower) and throwing a ball harder and harder horizontally. Ignore air resistance. The first ball might hit the ground (earth) 100m away. The second ball might hit the ground 100km away. The third ball might hit the ground 1000km away, well over the horizon and where the curvature of the earth is important. The fourth ball, if you throw it with exactly the right velocity, will just miss the earth all round, and come and hit you on the back of the head. It will have gone in a circular orbit. The fifth ball, with an even harder throw, goes in elliptical orbit, with you as the closest point. Note finally that if the earth was a small diameter, or if your tower or mountain was very high, that balls 1, 2 and 3, would travel in elliptical orbits with you at their furthest point. Phil -----Original Message----- From: phys-teach-talk-bounces at nzip.org.nz [mailto:phys-teach-talk-bounces at nzip.org.nz] On Behalf Of Rob Campbell Sent: Monday, 7 April 2008 10:34 p.m. To: 'Terry Moffat'; phys-teach-talk at nzip.org.nz Subject: RE: eliptical orbits Hi! Newton's explanation remains the simplest one that fully explains this, but I won't attempt maths in a text-only email! So, here's the hand-waving version. Earth satellites like the Moon or the ISS 'fall' toward Earth. They never arrive because there's a sideways component to their velocity. If the ISS really does move toward Earth, it loses PE and gains sideways KE. The sideways motion tends to draw it tangentially away from Earth - which doesn't prevent it coming closer (it does.) As it approaches Earth, tangential velocity builds up, slowing then reversing the Space Station's fall. It starts to rise, gaining PE as it does so, and losing KE. At its furthest point from Earth, its orbital velocity is lowest; at the nearest point, its orbital velocity is highest. This generates an ellipse, though at 10pm I can't illustrate this in words! A moment's thought will show that an ellipse is reasonable; 1/2 hour's thought with pen and paper will prove it. There's no difference in principle between a satellite orbiting Earth and a planet orbiting the Sun - just one of scale. Planets tend to follow elliptical orbits approximating to circles, maybe on account of their fiery origins. An ellipse is a squashed circle (apologies, mathematicians) with a major and minor axis rather than a constant radius. Really, a circle is the special case ellipse where the two axes are equal. Hope that helps, Rob Campbell -----Original Message----- From: phys-teach-talk-bounces at nzip.org.nz [mailto:phys-teach-talk-bounces at nzip.org.nz] On Behalf Of Terry Moffat Sent: Monday, 7 April 2008 8:22 a.m. To: phys-teach-talk at nzip.org.nz Subject: eliptical orbits Hi, can someone give me a simple reason why planets move in eliptical orbits. does it have something to do with the fact that the system is moving through space? ta Terry _______________________________________________ Phys-teach-talk mailing list Phys-teach-talk at nzip.org.nz http://nzip.org.nz/mailman/listinfo/phys-teach-talk_nzip.org.nz _______________________________________________ Phys-teach-talk mailing list Phys-teach-talk at nzip.org.nz http://nzip.org.nz/mailman/listinfo/phys-teach-talk_nzip.org.nz -------------- next part -------------- An HTML attachment was scrubbed... URL: http://nzip.org.nz/pipermail/phys-teach-talk_nzip.org.nz/attachments/20080408/42de839f/attachment-0001.html -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: image/gif Size: 84430 bytes Desc: image002.gif Url : http://nzip.org.nz/pipermail/phys-teach-talk_nzip.org.nz/attachments/20080408/42de839f/attachment-0001.gif From ki at kinim.co.nz Tue Apr 8 07:06:00 2008 From: ki at kinim.co.nz (ki) Date: Tue, 8 Apr 2008 23:06:00 +1200 Subject: eliptical orbits In-Reply-To: <468DDDC0BAEBD648821F71AF87A0284B07737BF6@cantwe2.canterbury.ac.nz> References: <47F9D991.DFDA.0008.0@rongotai.school.nz><000001c8989a$f1241b40$0301010a@robert972970e8> <468DDDC0BAEBD648821F71AF87A0284B07737BF6@cantwe2.canterbury.ac.nz> Message-ID: <000601c89968$8782e490$0201010a@kijy2q2bmrqo4t> Hi The shape of an elliptical orbit depends on the energy and angular momentum of the satellite. A mathematical analysis reveals that the ellipses two semi axes are given by and , where for a bound satellite. The special case of a circular orbit dictates certain requirements on and and this is not as easy to obtain as an elliptical orbit. A demonstration is possible with a 'conical pendulum' made to orbit under a central force. Keith Irvine AIC, Auckland _____ From: phys-teach-talk-bounces at nzip.org.nz [mailto:phys-teach-talk-bounces at nzip.org.nz] On Behalf Of Phil Butler Sent: Tuesday, April 08, 2008 9:43 AM To: Rob Campbell; Terry Moffat; phys-teach-talk at nzip.org.nz Subject: RE: eliptical orbits Hi all One of the nicest hand waving explanations is Newton's own figure which I have attached. I seem to recall that this email list doesn't take diagrams so it may be stripped off :-( The essence is to imagine standing on a tall hill (or the Auckland Sky Tower) and throwing a ball harder and harder horizontally. Ignore air resistance. The first ball might hit the ground (earth) 100m away. The second ball might hit the ground 100km away. The third ball might hit the ground 1000km away, well over the horizon and where the curvature of the earth is important. The fourth ball, if you throw it with exactly the right velocity, will just miss the earth all round, and come and hit you on the back of the head. It will have gone in a circular orbit. The fifth ball, with an even harder throw, goes in elliptical orbit, with you as the closest point. Note finally that if the earth was a small diameter, or if your tower or mountain was very high, that balls 1, 2 and 3, would travel in elliptical orbits with you at their furthest point. Phil -----Original Message----- From: phys-teach-talk-bounces at nzip.org.nz [mailto:phys-teach-talk-bounces at nzip.org.nz] On Behalf Of Rob Campbell Sent: Monday, 7 April 2008 10:34 p.m. To: 'Terry Moffat'; phys-teach-talk at nzip.org.nz Subject: RE: eliptical orbits Hi! Newton's explanation remains the simplest one that fully explains this, but I won't attempt maths in a text-only email! So, here's the hand-waving version. Earth satellites like the Moon or the ISS 'fall' toward Earth. They never arrive because there's a sideways component to their velocity. If the ISS really does move toward Earth, it loses PE and gains sideways KE. The sideways motion tends to draw it tangentially away from Earth - which doesn't prevent it coming closer (it does.) As it approaches Earth, tangential velocity builds up, slowing then reversing the Space Station's fall. It starts to rise, gaining PE as it does so, and losing KE. At its furthest point from Earth, its orbital velocity is lowest; at the nearest point, its orbital velocity is highest. This generates an ellipse, though at 10pm I can't illustrate this in words! A moment's thought will show that an ellipse is reasonable; 1/2 hour's thought with pen and paper will prove it. There's no difference in principle between a satellite orbiting Earth and a planet orbiting the Sun - just one of scale. Planets tend to follow elliptical orbits approximating to circles, maybe on account of their fiery origins. An ellipse is a squashed circle (apologies, mathematicians) with a major and minor axis rather than a constant radius. Really, a circle is the special case ellipse where the two axes are equal. Hope that helps, Rob Campbell -----Original Message----- From: phys-teach-talk-bounces at nzip.org.nz [mailto:phys-teach-talk-bounces at nzip.org.nz] On Behalf Of Terry Moffat Sent: Monday, 7 April 2008 8:22 a.m. To: phys-teach-talk at nzip.org.nz Subject: eliptical orbits Hi, can someone give me a simple reason why planets move in eliptical orbits. does it have something to do with the fact that the system is moving through space? ta Terry _______________________________________________ Phys-teach-talk mailing list Phys-teach-talk at nzip.org.nz http://nzip.org.nz/mailman/listinfo/phys-teach-talk_nzip.org.nz _______________________________________________ Phys-teach-talk mailing list Phys-teach-talk at nzip.org.nz http://nzip.org.nz/mailman/listinfo/phys-teach-talk_nzip.org.nz -------------- next part -------------- An HTML attachment was scrubbed... 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Name: not available Type: application/x-ms-wmz Size: 248 bytes Desc: not available Url : http://nzip.org.nz/pipermail/phys-teach-talk_nzip.org.nz/attachments/20080408/4ef9fe46/attachment-0009.bin -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: image/gif Size: 92 bytes Desc: not available Url : http://nzip.org.nz/pipermail/phys-teach-talk_nzip.org.nz/attachments/20080408/4ef9fe46/attachment-0010.gif -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: image/gif Size: 84430 bytes Desc: not available Url : http://nzip.org.nz/pipermail/phys-teach-talk_nzip.org.nz/attachments/20080408/4ef9fe46/attachment-0011.gif -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/octet-stream Size: 1577 bytes Desc: not available Url : http://nzip.org.nz/pipermail/phys-teach-talk_nzip.org.nz/attachments/20080408/4ef9fe46/attachment-0001.obj From dking at christscollege.com Fri Apr 11 15:41:39 2008 From: dking at christscollege.com (David King) Date: Sat, 12 Apr 2008 07:41:39 +1200 Subject: Great Resource Message-ID: This may be old news to some, but I have only just discovered it myself. http://www.freezeray.com/physics.htm or http://www.freezeray.com (if you want to see the bio/chem bits as well The swf files there are downloadable (although there is no download button) for educational/ non-profit etc. use. Some are a bit basic and a couple seem unfinished, but others are just great. You can build then into ppts or Notebook for SMART boards. Cheers David King Physics HoD Christ's College Private Bag 4900 Christchurch New Zealand -------------- next part -------------- An HTML attachment was scrubbed... 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