NO SUCH THING AS GRAVITY

[mooware]

<font color="yellow">You feel gravity very well when you fall off a cliff and break your neck.</font><br /><br />Unless you break the spinal cord at that point, then you may not feel a whole lot. That mother of all bowling balls would better qualify for "feeling" gravity.<br /><br />The effects of gravity are felt, and it's my understanding that things don't fall toward the earth, they are pulled. Hence leaping off a cliff, you are being pulled toward the center of the earth until you are abruptly stopped. Same with the bowling ball.<br /><br />Everything has its own gravity, even your cell phone. Albeit small.<br /><br /> Anything with mass distorts space around it.<br />

 

[CalliArcale]

The closest thing we have to being able to sense gravity directly is our internal accelerometers -- i.e. the semicircular canals. These are structures in the inner ear which detect acceleration. They are slanted so that the three canals follow three planes, perpendicular to one another, which allows the brain to correlate the directions indicated by each canal to determine the actual change in motion. Technically, they only measure changes in your head position, which is why you can stave off dizziness while spinning by doing as dancers do and turning your head opposite the motion of the turn and then rapidly snapping it around; it gives the canals a chance to settle between spins.<br /><br />When you are at rest, the canals allow you to have an instinctive knowledge of which way is down. (Your body does not rely on them exclusively; it also works by dead reckoning based on your body's position, which is constantly tracked by the cerebellum, and by visual cues. Motion sickness often occurs as a result of conflicting information from these sources, confusing your brain.) The canals are filled with a fluid and lined with tiny hairs. There are crystals floating in the fluid. The hairs detect the motion of the crystals floating in the fluid. When you are at rest, the crystals will settle on the bottom of the canals. This occurs due to an outside force acting upon them -- gravity. So in that case you are indeed directly sensing gravitational force.<br /><br />However, just as there are optical illusions, the semicircular canals can be fooled. They cannot distinguish between gravitational attraction and any other force which causes the head to accelerate. If you were in a rotating space station large enough to generate 1 G of acceleration, you will feel the same as if you were standing on Earth. Astronauts riding the space shuttle feel 3 Gs of acceleration with their semicircular canals, even though only 1 G of that is due to gravity. And of course in orbit, y <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[derekmcd]

"force" can be resisted. We can resist gravity.... hence... there is a force. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[rigel0509]

Think about this.<br /><br />What do you define as overall reality? If you define it by what you can see, feel, taste, smell, and hear, then what happens if you remove all five of your senses?<br /><br />By that ideal, 'reality' no longer exists. Your reality is in your mind at that point. Just because something cannot be observed with any of the five senses doesn't mean it does not exist, it simply means it is beyond human ability to percieve it within our sensual 'reality'.<br /><br />Can you see, feel, hear, smell, or taste an electron? No, but you can measure it, just like you can measure gravity.<br /><br />Besides, you can feel gravity anyway. It's called 'weight'.

 

[search]

Hello Tulip<br /><br />First lets clarify what FORCE is in PHYSICS which is the area GRAVITY is related to:<br />From Wiki:<br />"In physics, force is that which changes or tends to change the state of rest or motion of a body. As well as causing acceleration (a change in the body's change of motion) a force may also cause the body to distort (pressure) or turn (moment), thereby changing the body's state of rest."<br /><br />So when we say FORCE we do not mean: "MAY THE FORCE BE WITH YOU" Not some mythological force that we supposedly have.<br /><br />Gravity is a force which in physics just means that because of mass objects are attracted to each other (does not mean the fatter you are more girls/boys will fall in love with you).<br /><br />Now you are right when you say that we only know the effects. That is one of the greattest misteries of gravity. We know gravity because of the effects and we do know that the cause is mass. How GRAVITY FORCE is transmitted we only have theories.<br /><br />"According to Einstein's Theory of General Relativity, gravity is the curvature of space that results from a massive object. Think of a sheet of rubber with heavy marbles placed on it. The rubber around the marbles will be curved and smaller marbles placed nearby will roll toward the heavier ones. This is analogous to the way massive objects warp space. This warping is called gravity."<br /><br />Gravity related with Quantum Mechanics gets more complex:<br /><br />"In physics, the graviton is a hypothetical elementary particle that mediates the force of gravity in the framework of quantum field theory. If it exists, the graviton must be massless (because the gravitational force has unlimited range) and must have a spin of 2 (because gravity is a second-rank tensor field)."<br /><br />So you see that when we say GRAVITY IS A FORCE in GR we mean:<br />1. THERE IS A MASS<br />2. THE SPACETIME FABRIC IS DISRUPTED BY THAT MASS<br />3. OTHER MASS OBJECTS IN THAT SPACETIME ARE ATTRACTED TO THAT MASS<br></br>

 

[chubbs_wa]

I believe it's easier to dispute that there is no such thing as "Anti-Gravity".<br /><br />Gravity is a force you can easily determine .. simply because you don't slide off the Earth as it's rotating on its axis. "Zero-Gravity" refers to being weightless .. either in space or a vacuum.<br /><br />But I really don't believe in "Anti-Gravity" .. if someone actually made a space ship with some sort of anti-gravity drive .. wouldn't you go speeding off the Earth .. spinning out of the Solar system .. out of the galaxy .. out into the unknown universe? I mean .. Earth has gravity .. the sun has Earth in its gravity .. the Milky Way has our sun in it's gravity .. the universe itself spins with it's own gravity on our galaxy.<br /><br />Of course .. I've always wondered .. why everything in the Universe spins .. but that's a different subject!

 

[search]

Related to antigravity<br />Read<br />http://en.wikipedia.org/wiki/Anti-gravity<br />And also<br />click here (Wikipedia Talk: Anti-gravity)<br /><br />Boeing<br />http://news.bbc.co.uk/1/hi/sci/tech/2157975.stm <br /><br />Others sources<br />http://www.aeronautics.ru/archive/gravity/gravitsapa.htm<br /><br />(Edited for better thread display)

 

[qso1]

Zero gravity is more technically known as micro gravity because even in orbit, gravity still plays a role. But forawrd momentum plays a much greater role.<br /><br />As for anti-gravity. I always understood that to more or less mean taking the force of gravity and utilizing it to generate a counter force somehow. But I could be wrong about that. I often envisioned an anti gravity drive as something that would take gravity, amplify it and reverse its direction and using it in the same way that reaction mass is currently used in chemical rockets.<br /><br />The force of the anti gravity would borrow in a sense, from earth gravity so the vehicle borrowing could control the rate at which it departs from earth. In exchange, earth looses an equivalent amount of energy going around the sun. The amount so minute as to be virtually undetectable.<br /><br />Chubbs_WA:<br />the universe itself spins with it's own gravity on our galaxy.<br /><br />Me:<br />Actually, galaxies are the largest structures known to exist within the Universe and as such, rotate around their centers. The Universe does not rotate on our galaxy. Rather the Universe contains ours, and billions of other galaxies, quasars, etc. Science does not yet know what gravity actually is or where it originates, or why everything spins around its axis.<br /><br />Its also not known if or what the Universe spins, or spins around. We don't even know where the center of the Universe is. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[search]

Got to go but if you can remind me to come back to your last phrase:<br /><br />"Of course .. I've always wondered .. why everything in the Universe spins .. but that's a different subject!"

 

[qso1]

The good thing about it is that forums such as these allow us to put claims to the test. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[search]

Does anybody know any natural sky object that does not rotate?<br /><br />Why the rotation we observe (if anyone finds any good links I would like to read them):<br />http://curious.astro.cornell.edu/question.php?number=416<br />http://www.madsci.org/posts/archives/2000-03/953731806.As.r.html<br />http://www.newton.dep.anl.gov/askasci/ast99/ast99416.htm

 

[CalliArcale]

Done. Folks, try to be careful with long URLs. I find the easiest way is to make use of the "url" tags in UBBCode. It works like this (remove spaces when you do it):<br /><br />[ url =http://www.space.com]Link to SPACE.com[/url]<br /><br />Result:<br />Link to SPACE.com <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[qso1]

May have to do the same for posted image widths. I noticed wide images do the same as long URLs. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[yevaud]

I routinely resize all images I use to 500*500 or thereabouts. It's enough to be large, but not mess with the margins. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[ldyaidan]

Thanks! always wondered why some threads were really a pain! LOL<br /><br />Rae

 

[qso1]

I use 800 X 500 for most of my imagery anyway and it fits here okay. 800 wide, 500 high and jpeg them to lower percentages to reduce file size. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[junerian]

One theory I heard on gravity is this:<br />imagine time and space as a grid, and everything lies on this grid, and every body puts an indent on this grid (gravity). The bigger the indent the more gravity there is, and of course bigger objects make bigger indents. Thus we all have our gravity as well but it is a very very very small amount.<br /><br />Of course that's just one theory.

 

[oscar1]

Yes, but if bodies dent the grid, than there must be some sort of gravity under it to cause the denting.

 

[alokmohan]

Spacetime curvature causes gravity.

 

[witgenestone]

we call it gravity but we dont know much about it.

 

[delster45]

Could you elaborate a little on your perception or understanding of spacetime curvature?

 

[oscar1]

Yes, that's part of the General Relativity Theory, and solves the problem between Newton's and Einsteins' theories. However, if we can turn gravity into energy (like when accelerating spacecraft by means of fly-bys), the curvature of space-time would have to be more than a mere state or dimension. So I reckon that we are still missing something.