tag:blogger.com,1999:blog-8051630750074978974.post7467832416242670438..comments2023-12-19T09:40:12.020-08:00Comments on The Emoluments of Mars: Maurice Cotterell manages to be even more wrongexpathttp://www.blogger.com/profile/10369924104634464934noreply@blogger.comBlogger11125tag:blogger.com,1999:blog-8051630750074978974.post-25347465836487450272018-08-27T10:30:59.669-07:002018-08-27T10:30:59.669-07:00Hello Maurice old son. Have you thought of explain...Hello Maurice old son. Have you thought of explaining why 45% of Mars landers <i>don't</i> crash?expathttps://www.blogger.com/profile/10369924104634464934noreply@blogger.comtag:blogger.com,1999:blog-8051630750074978974.post-13185450879640159132018-08-27T08:24:39.489-07:002018-08-27T08:24:39.489-07:00Maurice: Thankyou for your comment. You wrote &quo...Maurice: Thankyou for your comment. You wrote "Newton failed to recognize, in his equation, that a falling body is also under the influence of 'centrifugal force' caused by the spinning of the Earth on its axis." That statement is wrong.<br /><br />Objects do not fall at the same speed, they fall at the same acceleration. The speed would entirely depend on the height from which they were dropped, would it not?<br /><br />As a B.Sc. honors graduate in electrical angineering, I do claim to understand the phenomena you say I do not. Admittedly I might have a hard time explaining them at this point, many years since I had to answer exam questions on those very topics. I do NOT proclaim myself an expert in these matters. You, however, do proclaim yourself one, and in that you are totally wrong. Your web page titled "How Gravity Works" is a demonstration of faulty mathematical reasoning that I cannot remember seeing bettered.<br /><br />I think the vitriol is coming in the direction <b>you > me</b> rather than the reverse. I feel no vitriol at all, I merely seek to counteract false statements posing as science and mathematics.martin blaisenoreply@blogger.comtag:blogger.com,1999:blog-8051630750074978974.post-76713746625934198022018-08-27T04:27:00.403-07:002018-08-27T04:27:00.403-07:00Martin Blaise does not understand why objects fall...Martin Blaise does not understand why objects fall to the ground (he does not understand how gravity works). I do. He cannot explain why objects fall at the same speed. I can. He does not understand how electricity works (why an electric current produces a magnetic field). I can. And he does not understand why a permanent magnet sticks to the 'fridge door. I do. And he cannot understand why 55% of Mars landers have crashed on Mars. I do. But he's a self-proclaimed expert on Gravity, spacecraft, and Mars. All of these things are explained on my my website www.MauriceCotterell.com. Fior the record: My article on Mars landers considers only spacecraft within the atmospheres of spinning planets (even if that atmosphere is only 1% that of the Earth). It is a pity that Martin Blaise cannot engage his brain before shooting-off his mouth with ill-considered vitriol; when the blind lead the blind, both shall finish-up in Martin Blaise's black-hole. No doubt he'll delete this because that's what coward's do.Maurice Cotterell.Maurice Cotterellhttps://www.blogger.com/profile/06882012745746853626noreply@blogger.comtag:blogger.com,1999:blog-8051630750074978974.post-27469629095555424712018-08-09T06:43:09.762-07:002018-08-09T06:43:09.762-07:00« It is a tricky concept. I now also (dis?)agree; ...« It is a tricky concept. I now also (dis?)agree; the satellite is also not subject to a centripetal force. But, if it was tethered to the planet by a long weightless rope, that was under tension due to holding the satellite in a lower orbit than it would naturally take... But orbiting naturally => no centripetal force...<br /><br />Ummm... Do you agree? »<br /><br />So long as "centripetal" is a misprint for "centrifugal", yes.expathttps://www.blogger.com/profile/10369924104634464934noreply@blogger.comtag:blogger.com,1999:blog-8051630750074978974.post-89747051006976518452018-08-08T19:07:11.259-07:002018-08-08T19:07:11.259-07:00Another thought!
Is an aeroplane flying through t...Another thought!<br /><br />Is an aeroplane flying through the atmosphere "attached to the planet"?<br /><br />For example, when performing spiral dives in a small plane. Gut-wrenching... I guess you get used to the feeling, but I never found it at all enjoyable.<br /><br />I don't think it's the attachment that matters, it's that the object is being forced to turn against "its will" by some external force.<br /><br />I think the reality is that centripetal force is only imaginary. It's just a variation on change of momentum.<br /><br />I'm finding it very confusing... Another example, the deflection of electrons by a magnetic field in a CRT. Is this any different from the satellite, or the steel on the edge of a flywheel?<br /><br />https://en.wikipedia.org/wiki/Centripetal_force<br /><br />seems to suggest not.<br /><br />Which brings me back to the naturally orbiting satellite.<br /><br />No wonder Cotterell doesn't understand it.<br />Two Percentnoreply@blogger.comtag:blogger.com,1999:blog-8051630750074978974.post-67913945576861915082018-08-08T18:39:54.910-07:002018-08-08T18:39:54.910-07:00Hi expat,
Like you, I've also been mulling th...Hi expat,<br /><br />Like you, I've also been mulling this problem over further since my previous post.<br /><br />I agree absolutely, it's a surprisingly complex problem.<br /><br />And I have to concede, I think you are right. I thought I had you, based on the static variables in the formula quoted, but I made a slight slipup. I took r to be fixed, but that's not really correct. As (the horizontal component of) the apple's velocity is tangential to the surface, r for the apple is increasing. That would result in a decreasing (magnitude-wise, i.e. less -ve) value for 'cf', which doesn't really add up either. So, I think that simply means the formula cannot be applied to an object that is (or would be) moving in a straight line.<br /><br />So, you are correct! Mr Apple is no longer subject to a centripetal force.<br /><br />It is a tricky concept. I now also (dis?)agree; the satellite is also not subject to a centripetal force. But, if it was tethered to the planet by a long weightless rope, that was under tension due to holding the satellite in a lower orbit than it would naturally take... But orbiting naturally => no centripetal force...<br /><br />Ummm... Do you agree?<br />Two Percentnoreply@blogger.comtag:blogger.com,1999:blog-8051630750074978974.post-42088888463967908282018-08-08T06:47:20.663-07:002018-08-08T06:47:20.663-07:00I think you're partly right there. I should no...I think you're partly right there. I should not have mentioned work. I just don't see a place for centrifugal force here. Gravity is providing the centripetal force needed to keep Mr. Satellite in orbit, and that's all there is.<br /><br />I've been thinking about the falling apple—a surprisingly complex problem—and here's what I've concluded:<br /><br />At the moment the apple detaches from the tree, it has an instantaneous Eastward velocity of 463 m/sec (this tree is at the equator). Per Newton's first law, it will continue that tangential velocity unless acted upon by some diverting force. <i>It is no longer constrained to follow a curving path</i>, as it was in the Good Old Days when it was attached to the tree. Accordingly, I say that Mr. Apple is not subject to the centrifugal force that the tree and everything else attached to the planet is.<br /><br />ergo, Cotterell is comprehensively wrong.expathttps://www.blogger.com/profile/10369924104634464934noreply@blogger.comtag:blogger.com,1999:blog-8051630750074978974.post-15592872215033602622018-08-07T16:30:05.479-07:002018-08-07T16:30:05.479-07:00expat wrote:
"Since the force actually does ...expat wrote:<br /><br />"<i>Since the force actually does work and moves something (the satellite) there's no requirement for an equal and opposite reaction.</i>"<br /><br />Huh!? You do mean 'work' in the sense of energy?<br /><br />If so, that's not correct. Otherwise, you have created a perpetual motion, over-unity machine. Where does the energy to do this work come from? Why does the satellite remain in orbit (unless it's impinging on the atmosphere)?<br /><br />There is no work, it's simply Conservation of Momentum. (And Conservation of Energy - no energy is being expended.)<br /><br />And there are, as always, equal and opposing forces. Gravity inwards, and 'centrifugal' force "outwards", in perfect balance. The satellite is not being worked on by either force, it's simply "sliding along" perpendicular to gravity, perpendicular to the 'centrifugal force', on an endless, frictionless elliptical 'track'.<br /><br />Isn't that correct?<br />Two Percentnoreply@blogger.comtag:blogger.com,1999:blog-8051630750074978974.post-3916862465965698132018-08-07T15:54:45.170-07:002018-08-07T15:54:45.170-07:00...and there's this:
https://mars.nasa.gov/mr......and there's this:<br /><br />https://mars.nasa.gov/mro/mission/timeline/mtaerobraking/expathttps://www.blogger.com/profile/10369924104634464934noreply@blogger.comtag:blogger.com,1999:blog-8051630750074978974.post-84689219007417111072018-08-07T15:49:47.589-07:002018-08-07T15:49:47.589-07:00«the apple you mention ... is also rotating with t...«the apple you mention ... is also rotating with the planet and does not suddenly "take off sideways" (i.e. cease its tangential motion) as soon as it starts to fall, it must continue to be subject to centripetal forces, surely?»<br /><br />I think not, or, if so, it would be its own centripetal force, not that of the planet.<br /><br />« Isn't this the exact same scenario as a satellite orbiting the Earth, continually falling in a curve towards the Earth. Isn't it 'centrifugal force' that's "keeping it up there"? »<br /><br />No, centripetal acceleration keeps it in orbit. Since the force actually does work and moves something (the satellite) there's no requirement for an equal and opposite reaction.<br /><br />« A planet of that size spinning that fast would never have formed (to that size) in the first place... »<br /><br />Sure, you're right. It's a whadjamacallit, a thought experiment. Thanks for the comments.<br />expathttps://www.blogger.com/profile/10369924104634464934noreply@blogger.comtag:blogger.com,1999:blog-8051630750074978974.post-73841235773031254402018-08-07T15:30:57.039-07:002018-08-07T15:30:57.039-07:00Interesting, thought provoking article, and thanks...Interesting, thought provoking article, and thanks for the formula.<br /><br /><br />But...<br /><br />Sorry, expat, maybe it's not just Cotterell who doesn't quite get this.<br /><br />Yes, a directly (perpendicularly to the landing point) approaching Lander, outside the planet's atmosphere cannot be affected by the 'centrifugal' force you discuss. (Note 2 accepted.)<br /><br />However, since the atmosphere rotates with the planet, and the apple you mention (at non-zero latitude) is also rotating with the planet and does not suddenly "take off sideways" (i.e. cease its tangential motion) as soon as it starts to fall, it must continue to be subject to centripetal forces, surely?<br /><br />Isn't this the exact same scenario as a satellite orbiting the Earth, continually falling in a curve towards the Earth. Isn't it 'centrifugal force' that's "keeping it up there"?<br /><br />Isn't the apple also momentarily "orbiting" - since it has a tangential velocity? Ok, so it's a very rapidly declining orbit, but won't that subtract slightly from g nevertheless? Surely, in order for the apple to fall at exactly g, it must have no tangential motion vector?<br /><br />[The apple maintains m and v, while r & L are fixed, therefore 'cf' is constant during the fall.]<br /><br />Which brings me to this:<br /><br />"<i>Statement 3 is also correct—it's perfectly possible to imagine a planet that rotates so rapidly that anything not tied down at its equator would be flung off into space. We would say that centrifugal force exceeds the force of gravity, in such a case.note 2</i>"<br /><br />I guess it's okay to imagine it - if your imagination is happy with the irreconcilable physics of it.<br /><br />A planet of that size spinning that fast would never have formed (to that size) in the first place... due to loss of matter into space. (It rhymes!)<br /><br />Of course, the real issue with landing on Mars is the lack of usable atmosphere, right? No free braking effect.<br />Two Percentnoreply@blogger.com