Started by randomvim, September 11, 2016, 03:14:56 AM
Quote from: Sal1981 on August 08, 2019, 02:45:54 PMMy gymnasium final project was in that in physics. I got what amounts to a C in grades :/ because I effed up the gravitational slingshot equations for it. We didn't have google back then.https://en.wikipedia.org/wiki/Gravity_assist
Quote from: josephpalazzo on August 08, 2019, 03:00:00 PMI see that you are prime candidate to buy my next book - Physics from Classical to Quantum, a self-teaching guide. Should be in store by Jan. 2020.Can I count on you?
Quote from: Sal1981 on August 08, 2019, 03:11:38 PMWouldn't hurt. I'd like a physical copy though.Last book that even came remotely close to a physics book was Hawkings' A Brief History of Time. Not exactly heavy on the physics part, as it was directed more towards layman understanding of physics.
Quote from: josephpalazzo on August 08, 2019, 02:56:31 PMSlight correction: rotation direction of the planet, not gravity... Civ2, that still exists??
Quote from: Cavebear on August 08, 2019, 03:29:37 PMSorry, I think of planets as gravity wells.
QuoteCiv2 exists if you can find a Windows 95/98 computer. I bought one online and it stays offline for safety. I might also buy a Commodore 64 because there were some really crappy quest games I would love to play again.
Quote from: josephpalazzo on August 08, 2019, 03:59:21 PMThat's fine as long as you don't mix up gravitational energy with rotational energy - not the same.I'm no longer into video games, though I was when the first pc's came out in the 80's- it was the only software available.
Quote from: Cavebear on August 08, 2019, 04:04:04 PMI'm still pecking at my brain about rotational energy. It wouldn't work with a perfectly spherical planet of completely uniform density, would it? Ignore centrifugal force on the planet.
Quote from: josephpalazzo on August 08, 2019, 05:00:36 PMNothing to do with "perfectly spherical planet of completely uniform density". Let me first take a simple scenario with no gravity involved. You are at rest (KE =0) in front of a merry go round. You step on it, holding to a handle or something. You now have rotational energy - the merry go round will slow down, however if there is an electrical input, that will compensate and keep the merry go round at constant angular speed. You and the merry go round are one body. Now you let go of the handle. You will fly out at a tangent with some velocity (KE â‰ 0). You just gained rotational energy. Of course, the merry go round would slow down, except for the electrical input. Now let's transfer that into outer space. The equivalent scenario is you orbiting around the earth with a velocity such that you are at rest with a fixed point on the surface of the earth, your house - GPS are satellites that do just that. You and the earth are one body. Now to let go, it's a bit more complicated than just letting go of the handle. You would need thrusters to escape the pull of gravity. Suppose you provide just enough energy to do that. Then as in the case of the merry go round, you will be propelled into space with rotational energy. Now think of the flyby object as it goes into orbit. At one point it's right over your house, the fixed point, and it has just enough energy to escape like you did. It will do exactly the same, it will be propelled with additional rotational energy. Hope this clear, if not, let me know what isn't clear.
Quote from: Cavebear on August 08, 2019, 05:39:33 PMWell, now is isn't, even more. I thought you were referring to a sort of density bulge that would apply a greater gravitational pull on any approaching body moving at a slower speed than the planetary rotation. Part of my confusion is that we are talking about a non-thrusting object that is not in orbit around a planetary mass, just passing by. I don't see how the rotating planet matters if it is not uniform. The passing object doesn't know or care about the volume or rotation of the mass below UNLESS it it is not uniform. Gravity is the only thing that will affect the passing object. If the planetary body is uniform is shape and density, the passing object react to it as a singularity.If the planetary object is NOT uniform, the passing object will react to the differences in mass as the body rotates and that will affect speed as the moon is affected by the rotation of the non-uniform Earth.So I still don't have an answer to my question.
Quote from: Cavebear on August 08, 2019, 01:38:01 PMSo you are saying a flyby has to be in the direction of planetary rotation?
Quote from: josephpalazzo on August 08, 2019, 06:48:40 PMThis is standard physics. In my textbook it would be done with equations, but would be the same explanation. I'm not only an author of physics book, but I also taught physics for 29 years, at college level. The only way to help you out is if you ask direct questions on the two scenarios I gave you. Meaning: clear your head of any preconceived ideas. Read it again line by line, and if anything is unclear, ask the appropriate question. That's what I've always told my students. The whole thing is about transfer of energy, particularly rotational energy, whether it's an ordinary object or the moon, the principle is the same. Gravity alone does not explain the slingshot effect. By the conservation of energy, the body would have the same energy when it leaves as when it entered into orbit, hence the same speed. So where does that extra energy come from? From the rotating planet. There is no other explanation.
Quote from: Cavebear on August 12, 2019, 06:48:46 AMThank you and I finally catch the error I sensed in your posts. You were talking about the rotational energy of the planet and I couldn't understand how that mattered unless the planet was non-uniform. It is the ORBITAL motion of the planet that gives the increased velocity to the object not the rotation.THAT makes sense.
Quote from: Cavebear on August 12, 2019, 06:48:46 AMIt is the ORBITAL motion of the planet that gives the increased velocity to the object not the rotation.THAT makes sense.
Quote from: aileron on August 12, 2019, 09:09:22 AMEqual and opposite reactions... Just think how much our space probes have altered the orbits of the planets already. ;)