surface gravity

[beilzabob]

If a planet made of pure Ununpentium with atomic weight of 288 was the same size of a planet made of pure hydrogen with atomic weight of 1.00794(7) would gravity have the same force onthe surface if you could hypothetically be on the surface? sorry for some of these dumb questions. I,m just a truck driver who thinks about these kinds of things while driving down the road 10 hours a day.Not much else to do but drive and think.

 

[igorsboss]

What do you mean, <font color="yellow">the same size</font><br /><br />If you mean "the same radius sphere", then this question all comes down to the average density of the planet.<br /><br />Of spheres of the equal radius, more dense planets will have more mass, and hence more gravitational acceleration at their surface than less dense ones.<br /><br />If you mean "the same mass sphere", then the gravitational attraction would be the same at the same distance.<br /><br />Density comes into play again, but in a different way. The more dense planet will have a smaller spherical radius. A smaller surface radius means a larger gravitational acceleration for the same mass planet.<br /><br />I would think Ununpentium would be more dense than Hydrogen, and so would have more gravitational acceleration at the surface, for either reason.

 

[beilzabob]

Thank you.So weight is what directly influences gravity,not size.

 

[tony873004]

Mass and size influence gravity. The formula is<br />g= GM/r^2<br />where G is 6.67e-11, M is the mass in kilograms of the planet, and r is the radius in meters.<br /><br />For example, Earth:<br />g = 6.67e-11 * 5.97e24 / 6371000^2 = 9.81 m/s

 

[nexium]

As the tony formula shows surface gravity is determined by mass and size = radius.<br />Density tends to increase with mass. Radius tends to increase with mass. So surface gravity tends to increase with density.<br />Density tends to increase with atomic weight, but there are some exceptions such as osmium = density 22: several elements have higher atomic weight, but somewhat lower density. Neil

 

[Saiph]

actually, density tends to drop with increased mass.<br /><br />Look at Saturn. Mass: 95x that of earth. Density: Less than water (~5x less dense). <br /><br />Basically composotion plays a huge role in the density. Saturn isn't very dense, as it's mostly hydrogen for instance, while the earth is silicates, aluminum, oxygen, etc. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>