Mass,gravity, and errmmm....

Layne Vakarian

Layne Vakarian
Now this has probably been asked before, but anyway:
If mass is what makes gravity, that is, mass attracts mass, the larger mass doing the larger share of the attraction can somebody please tell me why a planet with a mass equal to MORE than one earth-mass would have lower gravity than that of the Earth? Or a planet with a lower mass than that of the Earth would have gravity equal to that of the earth? For example I'm just out here at Traikoa IO-Z d13-286 3 and that planet has a mass of 0.82EM but a gravity of 1.0g.

Anyone?


Thanks :)
 

Vardaugas

Vardaugas
Distance? It's surface gravity, so if the diameter of the lighter planet is lower, thus density higher, you will have a different gravity at the surface. Acceleration of gravity is different in different place on earth, so it's not all that clear cut.
 

CMDR Redcrest

C
Silent Pact said:
Now this has probably been asked before, but anyway:
If mass is what makes gravity, that is, mass attracts mass, the larger mass doing the larger share of the attraction can somebody please tell me why a planet with a mass equal to MORE than one earth-mass would have lower gravity than that of the Earth? Or a planet with a lower mass than that of the Earth would have gravity equal to that of the earth? For example I'm just out here at Traikoa IO-Z d13-286 3 and that planet has a mass of 0.82EM but a gravity of 1.0g.

Anyone?


Thanks :)
Click to expand...
Off the top of my head:

Gravity is due to the rotational speed of a body around it's axis. The faster it spins the higher the gravity. That's my understanding anyway.
Lot's of very sciency folks about here would be able to explain it better I think.
 

Layne Vakarian

Layne Vakarian
Nope, not feeling it. If I'm say one million klicks away from an object its density isn't really a factor is it? It's still say a couple trillion tonnes of matter pulling on me. Whether its spread out over ten yards, ten miles, or a thousand miles isn't going to make that much of a difference is it? Or is it?

Vardaugas said:
Distance? It's surface gravity, so if the diameter of the lighter planet is lower, thus density higher, you will have a different gravity at the surface. Acceleration of gravity is different in different place on earth, so it's not all that clear cut.
Click to expand...
Ah. This sort of makes sense: Can I make the assumption that gravity at a planetary core is essentially zero then?
 

CMDR Zadian Lichtfrost

C
Silent Pact said:
Now this has probably been asked before, but anyway:
If mass is what makes gravity, that is, mass attracts mass, the larger mass doing the larger share of the attraction can somebody please tell me why a planet with a mass equal to MORE than one earth-mass would have lower gravity than that of the Earth? Or a planet with a lower mass than that of the Earth would have gravity equal to that of the earth? For example I'm just out here at Traikoa IO-Z d13-286 3 and that planet has a mass of 0.82EM but a gravity of 1.0g.

…
Click to expand...

The force is inversely proportional to the square of the distance between bodies.
The gravity that gets displayed is the gravity force at "sea level" (average surface?) of the body.
High mass but even bigger radius results in a lower gravity force at the surface.

Now everybody can go back at wondering why the force isn't inversely proportional to the cube of the distance…
 

Arry

Arry
Mass has little to do with 'volume' or 'weight'; but a lot to do with both.

The mass of something and therefore; in theory, its gravitational potential. Is based on how heavy it is, compared to its volume.
 

GreyAreaUK

GreyAreaUK
CMDR Redcrest said:
Off the top of my head:

Gravity is due to the rotational speed of a body around it's axis. The faster it spins the higher the gravity. That's my understanding anyway.
Click to expand...

What? No. No no no no no! I suspect you're thinking of centrifugal/centripetal force used to simulate gravity inside a rotating object.
 

Arry

Arry
Hossi said:
You forgot the diameter:

F=G*M1*M2/l²

If you are M1 and the planet ist M2 this means

a=F/M1=G*M2/l²

Traikoa IO-Z d13-286 3 has a diameter of 5,727km, compared to earths 6317km thats 89.9%
1/(0.899²)=1.23 times more gravity at same mass, or same gravity at 81% mass.
Click to expand...
....and that explains the avatar.
 

[VR] Deggial

[VR] Deggial
It's all about the distance from the mass center.
Gravity decreases with distance^2, which is quite fast.

A body with the same mass but larger radius will have a lesser gravitational pull on its surface.
A gas giant with a gigantic mass will have a zone with compfortable 1g closer to its surface than "expected".
 
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CMDR Redcrest

C
If you're talking about the effects of gravity of astral bodies when not on their surface:
Imagine your toilet flushing: the swirling water creates a force drawing things downward toward the centre.
The movement of astral bodies creates a similar effect though not perceivable (only through it's effects).
Different rotational speeds and mass creates a greater or lesser pull.
Larger objects disappear down the astral toilet faster than smaller ones who may lack sufficient density to be drawn in to the swirling vortex.

I hope this helps and is correct and not just a stream of my lavatorial consciousness! :eek:
 
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CMDR Zadian Lichtfrost

C
Silent Pact said:
…
Ah. This sort of makes sense: Can I make the assumption that gravity at a planetary core is essentially zero then?
Click to expand...

Yes and no. The core of an object is usually not it's gravitational centre. At it's core some gravity forces will be noticeable pointing to the gravitational centre. There the sum of all gravitational forces is indeed zero, but not because the diameter is zero. It's because the forces are pulling in all directions with the same force as all the mass is now around that point.
 

Frank

Frank
CMDR Redcrest said:
Off the top of my head:

Gravity is due to the rotational speed of a body around it's axis. The faster it spins the higher the gravity. That's my understanding anyway.
Lot's of very sciency folks about here would be able to explain it better I think.
Click to expand...

The rotational speed of the planet does actually play a role in the strength of the gravity, but quite a minor one, and the faster it goes the less gravity you get... at least at the equator.
 

Whitehair

W
Gravity effects fall off the further away you are from the mass. Even on the Earth gravity has slightly different values, when measured on top of a mountain as opposed to sea level.

Altitude

Gravity decreases with altitude as one rises above the Earth's surface because greater altitude means greater distance from the Earth's centre. All other things being equal, an increase in altitude from sea level to 9,000 metres (30,000 ft) causes a weight decrease of about 0.29%. (An additional factor affecting apparent weight is the decrease in air density at altitude, which lessens an object's buoyancy.[8] This would increase a person's apparent weight at an altitude of 9,000 metres by about 0.08%)

It is a common misconception that astronauts in orbit are weightless because they have flown high enough to escape the Earth's gravity. In fact, at an altitude of 400 kilometres (250 mi), equivalent to a typical orbit of the Space Shuttle, gravity is still nearly 90% as strong as at the Earth's surface.

The effect of ground elevation depends on the density of the ground (see Slab correction section). A person flying at 30 000 ft above sea level over mountains will feel more gravity than someone at the same elevation but over the sea. However, a person standing on the earth's surface feels less gravity when the elevation is higher.
Click to expand...

So, Density does play a role on planets, because a planet of lead will occupy less space than a planet of carbon. Meaning that the Carbon planet will have a greater radius, and therefore more distance from the centre of mass, and so less gravity effect at the surface because of that distance.
 
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CMDR Redcrest

C
Frank said:
The rotational speed of the planet does actually play a role in the strength of the gravity, but quite a minor one, and the faster it goes the less gravity you get... at least at the equator.
Click to expand...
Well it's nice not to be totally wrong! :D
I was always told that if Earth turned slightly slower we'd all float off into space. The water in a bucket tied to length of rope demonstrating centrifugal force type of thing.
 
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