Mars' gravity and mass compared to earth.

[ctrlaltdel]

I read on wikipedia that mars is 0.107 earth masses, but it's surface gravity is 0.37g. If it only weighs a tenth of the earth, why isn't its surface gravity a tenth of a G?

 

[heyscottie]

Because its radius is also smaller -- about .533 earth radii.<br /><br />The equation for gravity is F = G*m1*m2/(r^2).<br /><br />We can get rid of G because we are doing relative calculations here.<br /><br />F = .107*m2/(.533*.533)<br /><br />F = m*.377<br /><br />Here we see that acceleration due to gravity is about .377 * earth's at the surface.

 

[ctrlaltdel]

Equations go over my head. Are you saying that radius has an effect because a large low density body would place a person futher up the gravity well and therefore gravity's effect would have fallen off than if it was a small planet with equal mass?

 

[MeteorWayne]

Basically, yes, you've got it right. Since you are on surface, on mars you are actually closer to the center of mass than you are on the earth. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[heyscottie]

Exactly. The further you go from something, the less its gravity can affect you. You are further from the center of Earth than you would be from the center of Mars, so that gets factored in.<br /><br />The same applies on the moon. It is only .01 times the mass of Earth, but its gravity is about 1/6 that of Earth. Why? Because its radius is so much smaller -- about .27 times that of Earth.<br /><br />Once again,<br />F = .01*m2/(.27^2)<br />F = m2*.166<br /><br />Scott

 

[3488]

Interesting note to add. The surface gravity of the planet Mercury is identical to that of Mars.<br /><br />Mercury is smaller & less massive than Mars (Mercury 5.6 % as against 11% for Mars, of Earth mass), but its density is very much greater (possibly a huge iron core surrounded by a silicate mantle & crust), about 5.3g/cm3, against 3.9g/cm3 for Mars.<br /><br />Using the formula (if I have not screwed up).<br />F = .056*m2/(.38^2) <br />F = m2*.377.<br /><br />Andrew Brown.<br /> <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[weeman]

Very interesting stuff. It was a good question to ask ctrlaltdel. <br /><br />How far out would you have to be from the center of mass of Jupiter or Saturn to effectively feel the same amount of gravity as on Earth? <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>

 

[3488]

Jupiter @ the 1 Bar level in its atmosphere, the gravity is 2.65 that of Earth & that of Saturn @ the 1 Bar level in its atmosphere is 1.17 that of Earth. The same for Uranus is 0.93 & Neptune 1.12.<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[ctrlaltdel]

Thanks for the explanations, it doesn't seem so counterintuitive now <img src="/images/icons/wink.gif" />

 

[MeteorWayne]

This was a great thread, thanx for starting it, and welcome to the community. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[why06]

ctrlaltdel,<br /><br />I can't type your name without the Windows task manager popping up. ( I think everyone has already figured this out, but someone had to say it)<br /><br />BTW: welcome to SDC. I learned something new as well. We could use an attention to detail like that here. Especially when many others here tend to state facts without sufficient knowledge of why or how that is so. (me being one of them 50% of the time) <img src="/images/icons/wink.gif" /><br /><br />Again welcome. I hope you stick around <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[derekmcd]

It's all about the inverse square law and density. If you compacted the earth to the size of a baseball, but remained the same distance (radius) from the center of mass, you would feel no difference in the effect of gravity. However... stand on that same baseball and you would be crushed. <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>

 

[why06]

FYI: If earth was the size of a baseball it would be a black hole. And you detect a considerable difference in gravitational strength. <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[yevaud]

Not until you got very close to it. At a distance, it's gravity is no different than Earth's at that distance. For something as small (mass) as Earth, you'd have to get within a few thousand miles of it for the true gravitational effects to occur. <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>

 

[why06]

However the exponential graph of the increase of gravity would be more sharp. Standing t or near the center of the earth would be different from stand atin the same space with the black hole ther, but I get your point. At an distance the effect of gravity will either remane at its original strenghth or more likely drastically decrease at greater distances e.g. "where earths surface used to be. There would still be the same amount of gravity, but the way it would be distributed as far Distance/ Force would much difference.<br /><br />In fact Im thinking that the black hole may be all, but undetectable at that distance from it center based on the activities of many black holes. <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[derekmcd]

FYI: The schwarzschild radius for the Earth is 9 millimeters which is about 3/8 of an inch. As for the gravitational strength, I think Yevaud got ya squared away on that. <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>

 

[why06]

Post deleted by why06 <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[why06]

I did a search and Yevaud is damned right. It seems as if we feel the most grvitation on the surface, but a blackhole has the most gravitation on its surface as well. So if we were to dig into the center of Earth we would have considerably less mass. However the force of gravity would be just as strong at surface distance as it is the same distance away from a black hole. The is the turning point however. From there farther in or farther away the forces of gravity are not the same between the Earth and blackhole.<br /><br />From: http://amazing-space.stsci.edu/resources/explorations/blackholes/teacher/sciencebackground.html<br /><blockquote><font class="small">In reply to:</font><hr /><p><i>For example, the surface of the Earth where we are standing is 6378 km from the center of the Earth. The surface is as close as you can get and still be exposed to the total mass of the Earth. Thus, it is where you will feel the strongest gravity. If suddenly the Earth became a black hole (impossible!) and you remained at 6378 km from the new Earth-black hole, you would feel the same pull of gravity as you do today. For example, if you normally weigh 120 lbs, you would still weigh 120 lbs. The mass of the Earth hasn't changed, your distance from it hasn't changed, and therefore you would experience the same gravitational force as you feel on the surface of normal Earth. But with the Earth-black hole, it would be possible for you to get closer to the total mass of the Earth. Let's say that you weigh 120 lbs standing on the surface of normal Earth. As you venture closer toward the Earth-black hole you would feel a stronger and stronger force. If you went to within 3189 km (half the radius of normal Earth) of the Earth-black hole you would weigh 480 lbs! For the same exercise with the Earth as we normally experience it, if you dug your way to 3189 km of the center,</i></p></blockquote> <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>

 

[MeteorWayne]

Yevaud is usually damned right. Even when he's wrong <img src="/images/icons/wink.gif" /> , he sticks to the case. That's all one can ask.<br /><br />He has a heck of an event horizon <img src="/images/icons/laugh.gif" /><br /><br />One of many points here (the thread is oscillating) is that if the mass of the sun is a star as it is now, or a black hole of the same mass, at our distance, there's not much difference.<br />Mercury might be more problematic. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[alokmohan]

For a black hole of mass of sun mercurys position is same.

 

[bdewoody]

I have another related question. Does the spin rate of a planet have an effect on the surface gravity? <div class="Discussion_UserSignature"> <em><font size="2">Bob DeWoody</font></em> </div>

 

[nexium]

The spin of a planet has the effect of reducing the gravity near the equator typically by 1% or less. For a low gravity body such as an asteroid the equitoral gravity can be reduced to zero by the spin, but the asteroid is likely to break up. Neil