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So is this centrifugal force counteracting gravity? So then gravity would be like your hand's grip preventing the bucket from flying away when you swing a buck
by barking 13y ago
So is this centrifugal force counteracting gravity?
So then gravity would be like your hand's grip preventing the bucket from flying away when you swing a bucket of water?
If this is the case then I think I'd understand the way planets don't fall into the sun better. The way I've heard it described before as something like 'forever falling into the sun' confusing.
- jacquesm 13y agoIt's actually a very gradual spiraling inward. This is because the momentum imparted initially is slowly dissipated (by impacts & interaction with the gravitational field of the sun), an extremely small factor. The question is whether the sun will go nova before or after we (or our sterilized remains) finally arrive :) That's not the only effect, all of this is counteracted by the decrease in mass of the sun and the tidal interaction between the sun and its planets (which slows down the rotation of the sun), both of these should push the earth outward from the sun. I'm not sure how it all works out (whether it is a net positive or a net negative) but it can't be much or we'd have drifted out of the zone where life is sustainable long ago.
- barking 13y agoThanks. I can understand the mass of the sun having an effect but why would the speed of rotation of the sun have an effect on earth's orbit?
- jacquesm 13y agoI think that's this effect: http://en.wikipedia.org/wiki/Tidal_acceleration http://en.wikipedia.org/wiki/Tidal_acceleration Speaking about the rotation of a gaseous body is a bit tricky anyway, not all parts of the sun rotate equally fast. (inside/outside, equatorial/polar).
- barking 13y agoThat's a very interesting link, the diagram of the earth moon system explains it quite well, I think. I just googled and found this article that reports the same effect between the earth and the sun http://www.newscientist.com/article/dn17228-why-is-the-earth-moving-away-from-the-sun.html#.UjbUUX_JLIc http://www.newscientist.com/article/dn17228-why-is-the-earth...
- deleted 13y ago[deleted]
- jlgreco 13y agoTidal forces between the Earth and its Moon in fact result in the Moon (very slowly) getting further and further away from the earth.
- jacquesm 13y agoYep. The actual experimental verification of this makes for very interesting reading. see: http://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiment http://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiment and lots of links referenced from there. Amazing precision, I still find it quite incredible that such a distance could be reliably measured to such precision and that meaningful conclusions could be drawn from those measurements.
- jonmrodriguez 13y agoYes, I think you're correct
- barking 13y agoYay me!
- jlgreco 13y ago> So is this centrifugal force counteracting gravity? I think that is probably a relatively reasonable way of considering it, but to be clear, centrifugal force isn't actually something that exists. It wouldn't be drawn in a free body diagram unless the diagram was drawn with a non-inertial reference frame, but even then it is only drawn so that equations meant for inertial reference frames will still work. (http://en.wikipedia.org/wiki/Centrifugal_force_(rotating_reference_frame) http://en.wikipedia.org/wiki/Centrifugal_force_(rotating_ref...) I think the best way to get an intuitive understanding of how orbit works is with Newton's cannonball thought experiment, and perhaps playing around with a simulation of it.
- barking 13y agoThanks I looked it up on wikipedia and they have a nice simulation there. http://en.wikipedia.org/wiki/Newton%27s_cannonball http://en.wikipedia.org/wiki/Newton%27s_cannonball I didn't understand the elliptical orbit at first and was writing a supplementary question here but as i did so the following explanation occurred to me. As it spirals outward it's no longer travelling at right angles to the force of gravity so now gravity exerts some force parallel and opposite to its direction of travel and starts to slow it down. It slows down at a rate greater than the required orbital speed does and eventually it's travelling at less than orbital speed and starts to travelling closer to earth again and now gravity starts to act to increase its speed because the ball is again not travelling perpendicular to the force of gravity but this time gravity's pull increases its speed. Now the ball's speed increases faster than the required orbital speed does until it exceeds orbital speed again. And so ad infinatum!