You are absolutely right, these cases are at the edge of sense: there's really no way to escape from gravity, except as Nate said, beeing on a Lagrange point and beyond, far from the earth.
Neutral lift/bouyancy when ballooning/diving - a state at which you neither rise nor fall with respect to the Earth? Just a thought... ---------- www.myspace.com/markburness
1° No french (or belgian) forum about harp would have accept this discussion that's maybe the biggest OT encounterable. I thank the moderators or admin's to allow this, and you guys to discuss about this all: you're all outstandingly open minded, and that's what I wanted to experiment by enrolling me on this forum: I'm really amazed by your behaviour and interest, and certainly not disappointed. 2° I'd like to answer to Verylong that gravity force depends on existing masses, as I said about apples here above, and that his last two lines could be interesting to argue about. 3° What do you think if we come back to our main interest, i.e. harp, because I'm afraid we could push some people on the edge... Don't forget I'd really like to shortly soon speak about a very soon, but very seldom phenomenon that's not theory and links to astronomy, and don't want to exaggerate with OT: the extent we live here was certainly not expected by the initiator of this topic. Astronomy is a great interest for me -and maybe for some people here- and so, we could be going on for... weeks? Let's refrain, except if you really want to keep on! Thanks again to moderators!!!!!!!!!!!
5F6H, buoyancy in sea or atmosphere is the same "illusion" as floating in a shaft. Seas and atmosphere are elements that are hold sticked by gravity. A flying bird escapes gravity only in poetry: what happens actually if he stops flying? Whatever happen in atmosphere or sea is influenced by gravity, and beyond our atmosphere, orbiting is by essence part of gravity's influence and more, is DUE to gravity.
Last Edited by on May 08, 2012 2:06 PM
Enough levity. Back to gravity. A question I have been wondering about for years is how fast does gravitational force act? Is it just there or does it act at the speed of light, say? Thought experiment: if a massive black hole formed one light year away, would I feel the effect immediately, or would it take a year? Is there a Belgian opinion on this subject?
The slinky experiment shows the speed of the wave of tension being released. Gravity acts similarly, only at the speed of light. In Newtonian physics it was assumed to move instantly, but then quantum physics came along with it's silly speed limits. Really, 186,000 miles per second? In the left lane? :)
The interesting thing about that video is that when you start applying it's concepts to other objects you realize that a tension wave occurs in every object you dangle, but the speed at which it propagates is very different. If you dangle a 2x4 by one end and drop it, technically the top end would start falling first, since it's creating the tension.
I saw another video about event horizons of black holes. Apparently the science says that if you were watching someone cross the event horizon they would appear to slow down, stop, then slowly fade away. I can't find that video though.
Bronze, That's a good question; not really an opinion, but theories which are rather well admitted by scientists and digested by myself. 1° Black hole at 1 lightyear from the earth: we likely wouldn't be there to speak about. In the center of our galaxy (and probably the same for billions galaxies existing) could be lodged a blackhole that holds moving around itself the whole mass of about 100 billions stars -only for our galaxy, that extends to about 100.000 lightyears -stars which are "a minima" like our sun (= 1 million times the volume of the earth) and could each, own a "solar" system = exoplanets. Naturally are the photons swallowed by the black hole, hence the name. 2° The "modern" theory of gravity doesn't speak about forces like we did, but about space's curvature (Einstein's) whose range depends on the (group of)bodies's mass. Now at a local scale (e.g. our very very small solar system) we can without mistake speak about forces, which seem to be progressive, depending on the speed's bodie's mass evolving ( I evoke notably the birth of new stars in the nebulae's core -that's still a local system). Depending on the existing dust and hydrogen density in the area where "something" starts the birth's process, the gravity will take place, but I believe no one could say at which speed and range, nor when the process will end, just: will it produce giant stars (like Antares or Betelgeuse) or mundane stars (like our sun)? 3° Now the gravity of the sun pretty attracts and blazes comets whose orbits are too close of him, it means that the force is infinitely more powerful than the earth's one: thus a blackhole would attract less massive bodies at which speed? Nobody knows, but extrapolation would theoretically give attraction speeds which have nothing in common with our kind and well known lightspeed: I suppose a weak mass e.g. our sun and all the planets beeing attracted by a black hole...in an obviously strictly unknown context. We know that our Milky Way and Andromeda galaxy (about 2 millions lightyears from us) are attracting each other at a gentle speed of 400.000 km/h. Scientists say that these galaxies actually "rush" to a close encounter that's expected in...3 billions years.
Last Edited by on May 08, 2012 7:58 PM
Thanks laurent for your comprehensive explanation. I used to worry about the fate of the universe, but then I realized there ain't much I can do about it, like the weather...
We have just returned from a looong weekend at our beach house. The weekend was beautiful but sad for members of our small community at Peregian Beach because a visitor going for a swim on Sunday, went missing, & a huge search commenced culminating in his body being washed ashore on Wednesday morning.
It's a beautiful beach but unless one is an experienced swimmer able to read & understand the conditions it can be very dangerous. There are patrolled areas with Surf Lifesavers & the message is strong to only swim in flagged/patrolled areas. Sadly some visitors are unaware of the non binding 'rules' and take risks. This happened to a 37yo father of 2 who left his wife on the beach for a final swim before he was to drive back to Brisbane.
The scenes of sunrise were taken this morning only minutes after his body was washed ashore. I was not a witness but in the distance ca 1k I could see all the lights on the beach. The last clip was of the super moon taken last Sunday evening the day the man went missing/drowned.
It was not until I started making this video that all the above registered with me as meaning something. I had the MP3 of Wayfaring Stranger done weeks back & have been looking for suitable shots. The MP3 is good but somehow the sound on Youtube is a bit distorted if volume is high.
@ Bronzewailer "Thought experiment: if a massive black hole formed one light year away, would I feel the effect immediately, or would it take a year? Is there a Belgian opinion on this subject?"
A black hole, theoretically (no one has ever seen one), is a collapsed star. So there would have to have been a huge star where the huge black hole formed. If we had survived the fact that there as such a huge star 1 light year away AND survived the explosion when the star went supernova & fast forward to the presence of the black hole ...we would feel no difference gravity-wise to when the star had been there. A black hole only has the mass of the star that formed it. E.g. if our sun turned into a black hole (general consensus is that it does not have enough mass to do this, it is proposed that it will become a white dwarf), then that black hole would exert the same gravitational force as the sun does now.
Black holes only look like "holes" because light cannot escape, they are probably more like, dense black orbs (reckoned to be the most perfect spheres). However, most people's understanding of black holes seems to be gleaned from the Disney movie of the same name ;-)
5F6H, I evoked what we call "super massive" black holes, that have 1/700th of the galaxy's bulb's mass! We'll know more about them thanks to the 62-working-together radiotelescopes in Atacame, Chili, who naturally operates in radio waves (AMA I think). These black holes are incredible monsters and I dont' know if physics works normally in their neighbourhood!
I am aware of the theory of super massive black holes, the point being that even if black holes do not exist, at the centre of the galaxy you still have objects of vast mass (super massive stars?) coalescing. Black holes, or no, not a good place to vacation.
The layman's perception of black holes is that they dash about the galaxy, hoovering up worlds, like a giant, intergalactic Pac Man, popping open gateways to planets populated by blue skinned Amazonian women demanding to know more about "this Earth thing you call kissing?" Of course, only part of this is true... ---------- www.myspace.com/markburness
Yes Miles, right! Now the AMA observatory detects super massive black holes vomiting light (i.e. plasma) and "feeding" a galaxy. You'll see that one day, scientists will say that "Big Bang" (hey Bronze, a belgian theory!) was a super-super massive black hole...
Last Edited by on May 09, 2012 5:15 AM
@ Miles "The trick to measuring "invisible" things is observing its effects on the material around it."
Indeed....
:-)
Black holes might well explain what is being observed, but no one has ever seen one, nor an image of one (that wasn't an artist's impression). ---------- www.myspace.com/markburness
Interesting tangent folks. Thanks for all the info and insights. You've made things clearer in my brain. I'm gonna refrain from further questions and speculations now. Back to the )harmonica) woodshed...
