Why are planets spherical?

[lastleg]

I am curious to know why all of the planets/stars are spherical (or close to it). Thanks

 

[harmonicaman]

That's because of the nature of gravity. You can think of gravity as a force that points inward toward the center of the planet so that every part of the surface is pulled evenly toward the center, resulting in a spherical shape. <br /><br />Of course, planets are not perfect spheres because mountains and valleys and even skyscrapers are all deviations from the spherical shape. However, as planets get larger, gravity gets stronger, until eventually large objects on the surface are crushed under their own weight. That's why we don't have mountains that are 50 miles high or skyscrapers that are 2,000 stories tall. Planets stay basically spherical because any large deviations get crushed. <br /><br />Although gravity keeps planets close to spherical, there are other forces that cause deviations from the basic spherical shape. For example, the rotation of the earth once every 24 hours, causes an apparent centrifugal force which creates a bulge at the equator. In fact the earth's diameter at the equator is 7,926 miles while the diameter between the poles is only 7,900. <br /><br />

 

[bonzelite]

it is because of the nature of planetary expansion from it's center of mass, outwardly, creating an acceleration upon all bodies resting upon it's surface or orbiting it's surface. there is no gravity acting upon the planets.

 

[robnissen]

"it is because of the nature of planetary expansion from it's center of mass, outwardly, creating an acceleration upon all bodies resting upon it's surface or orbiting it's surface. there is no gravity acting upon the planets. "<br /><br />Yawn. I sure am glad Bonz is here to protect us from that whack job Newton.

 

[bonzelite]

yep. gravity is, in my opinion, an erroneous and totally un-necessary idea.

 

[spacefire]

then...how do you explain the gravity gun in HalfLife 2? <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[bonzelite]

is that a first-person shooter PlayStation game?

 

[the_wizard]

"it is because of the nature of planetary expansion from it's center of mass, outwardly, creating an acceleration upon all bodies resting upon it's surface or orbiting it's surface. there is no gravity acting upon the planets."<br /><br />So if we jumped we wouldnt be resting on the surface and should float freely? We would never land.... bad theory you have there.<br /><br /><br />

 

[bonzelite]

<font color="yellow"><br />So if we jumped we wouldnt be resting on the surface and should float freely? We would never land.... bad theory you have there. <br /></font><br /><br />no. you're not following. <br /><br />i said objects are resting upon the surface due to the acceleration of expansion. we jump up, the earth expands to meet us, and we hit the ground. there is no gravity whatsoever. it is acceleration only. geometric.

 

[the_wizard]

"i said objects are resting upon the surface due to the acceleration of expansion. we jump up, the earth expands to meet us, and we hit the ground. there is no gravity whatsoever. it is acceleration only. geometric. "<br /><br />So if the person next to me doesn't jump will their legs be crushed as the earth rushes up to meet me?<br />

 

[dragon04]

<font color="yellow">said objects are resting upon the surface due to the acceleration of expansion. we jump up, the earth expands to meet us, and we hit the ground. there is no gravity whatsoever. it is acceleration only. geometric.</font><br /><br />You're joking, right? <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

 

[bonzelite]

<font color="yellow"><br />So if the person next to me doesn't jump will their legs be crushed as the earth rushes up to meet me? </font><br /><br />i don't quite understand your statement. but the acceleration is 9.8m/s² --the known "force" for earth's gravity. nothing is crushed unless you jump from a building. in that case, depending on how high you are, you could break your legs or die, unless you had a parachute. nothing is any different as an effect upon the body. it's just that in my premise "gravity" does not actually exist, only acceleration due to expansion. gravity is not necessary mathematically. or actually.

 

[bonzelite]

<font color="yellow"><br />You're joking, right?</font><br /><br />no.

 

[why06]

basically what he is saying is since every thing expands at the same rate you ccould not tell the earth is catching up to you because the space in between th earth and you would also increase. <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[rrl2]

give me my flashdrive!

 

[CalliArcale]

I don't think that's what he means. bonzelite is a proponent of a steady-state universe and has repeatedly spoken against the idea of expanding spacetime. Unless I'm greatly misunderstanding him, that is, and I trust he'll speak up to correct me if I've gotten this wrong. <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>

 

[yevaud]

Pardon me, RRL2, but that's the second time you've said that now, in two different threads.<br /><br />Care to explain what you mean by that? <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>

 

[the_wizard]

<blockquote><font class="small">In reply to:</font><hr /><p>i don't quite understand your statement. but the acceleration is 9.8m/s2 --the known "force" for earth's gravity. nothing is crushed unless you jump from a building. in that case, depending on how high you are, you could break your legs or die, unless you had a parachute. nothing is any different as an effect upon the body. it's just that in my premise "gravity" does not actually exist, only acceleration due to expansion. gravity is not necessary mathematically. or actually. <p><hr /></p></p></blockquote><br /><br /><b>So if the earth is expanding at a known constant as you state, why is it the same size that it always has been. Its not getting bigger, therefore its not expanding[/color]</b>

 

[harmonicaman]

<b>The_Wizard -</b><br /><br /><b>Bonzelite's</b> idea that everything is blowing up so the earth and other bodies are catching up to the objects has been put forth several times, but a bit of thinking should convince you that things can't work that way. <br /><br />Try to explain how an object can stay in orbit - i.e., if a satellite is above NY at one moment, it cannot get to another part of the globe and be the same distance above the surface unless it moves in a curved path - so if the earth were merely rising to meet the satellite at an accelerating rate - the satellite is not going to appear as being in an orbit that circumscribes the earth. <br /><br />That being said; there're other theories of gravity based upon some sort of accelerating dynamic - one that has found favor with relativity dissidents is the inflow theory -- the notion being that space is falling into matter -- the greater the density of the mass the greater the inflow rate. <br /><br />This theory cannot be so easily dismissed - it has some merit in that it relates the time dilatation that is consequent to motion in special relativity to the amount of time dilation that is measured between clocks at different gravitational potentials - so a clock at the earth's surface runs slower than a clock at an altitude of 1000 meters by exactly the same factor as would be measured if space were falling inwardly and the spatial velocity were increasing as you got closer to the earth in proportion to a factor which corresponds to the escape velocity.<br /><br />There are also dynamic theories that relate the magnitude of the gravitational constant to the rate of expansion of the universe - these are based upon a spherical model of the universe that is expanding in accordance with Hubble's law -- when a sphere dilates at a constant radial rate the volume increases geometrically (as the cube of the radius)... In other words, the volume is accelerating and the magnitude of that acceleration corresponds to G (which

 

[CalliArcale]

Objects which bulge at the equator due to rotation are said to be oblate. (Yes, I know you know that, steve, I'm saying it for the benefit of those who don't. <img src="/images/icons/wink.gif" /> ) The Earth is oblate. But one major planet is so oblate that the effect is easily discernible by the human eye: Saturn. You might think it looks ovoid because of the rings, but it's more than just the rings -- Saturn is significantly flattened. <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>

 

[drwayne]

Oblate spheroid is one of those sets of words that will make you popular at parties. <img src="/images/icons/wink.gif" /><br /><br />Actually, knowing when in ballistic modeling you can use the flat Earth approximation, the spherical Earth approximation, or have to go to something like the World Geodetic System (WGS) models, you will be popular with the 6DOF crowd at work.<br /><br />Wayne<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[drwayne]

In case you are not bored yet:<br /><br />http://en.wikipedia.org/wiki/WGS84 <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[yevaud]

Yes, once described to me by a Professor as the "Fat Man sitting on a Beachball" effect.<br /><br /><img src="/images/icons/smile.gif" /> <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>

 

[dragon04]

I have an idea. On Earth Day, let's get all 6 or so billion of us to jump up and down for an hour or so.<br /><br />We could expand the Earth and solve this pesky overpopulation problem!<br /><br />You're Welcome.<br /><br />Sincerely,<br /><br />The Fix It Guy <div class="Discussion_UserSignature"> <em>"2012.. Year of the Dragon!! Get on the Dragon Wagon!".</em> </div>

 

[cygnusx1111]

The reason is because a sphere contains the most volume with the min. amount of surface area.