Solving for Gravity Without Gravitational Constant - Little g vs Big G

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In summary, the conversation revolved around finding a method to solve for the gravity of a planetary body without using the gravitational constant. Various methods were suggested, such as using the orbits of satellites or measuring the acceleration of a dropped object. The original poster also mentioned that they had found a unique method for calculating gravity without the use of the gravitational constant and wanted to confirm its validity before submitting it for publication. However, it was noted that the Physics Forums is not a platform for discussing personal speculations or original research, and the thread was closed.
  • #1
Deleted member 658453
Anyone know of a way to solve for gravity of a planetary body without using the gravitational constant?
 
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  • #2
Use orbits of its moons or other satellites. That gives you ##GM## which you can then use to get ##GM/r^2## for any ##r##. No need to find ##G## or ##M## independently.
 
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  • #3
What if no satelites to measure?
 
  • #4
JD Duncan said:
Anyone know of a way to solve for gravity ...
Solve what? You haven't stated what is given.
 
  • #5
It’s not a specific value calculation. I’m asking about method. Do you know of a way to find a body’s gravity, in equation form perhaps, without using the gravitational constant to find the answer.
 
  • #6
Any measure of ##g## at a known ##r## gives you ##GM## and let's you deduce ##g## at any given ##r## outside the body. You need to work quite hard to get ##M## and ##G## separately.
 
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JD Duncan said:
It’s not a specific value calculation. I’m asking about method. Do you know of a way to find a body’s gravity, in equation form perhaps, without using the gravitational constant to find the answer.
You were given a method and you rejected it because you said the information needed wasn't available. Are you going to give the same response for any method given? What information is available? We can't answer the question if you won't tell us the constraints.
 
  • #8
russ_watters said:
You were given a method and you rejected it because you said the information needed wasn't available. Are you going to give the same response for any method given? What information is available? We can't answer the question if you won't tell us the constraints.
Where you coming from? I haven’t rejected anything. It’s a general question, not a specific problem. No other info needed.
 
  • #9
JD Duncan said:
... without using the gravitational constant to find the answer.
But what can be used?
 
  • #10
that’s what i’m asking...do you know any other parameter combinations, any other method of any nature, any other equation that finds gravity without big G?
 
  • #11
JD Duncan said:
Where you coming from? I haven’t rejected anything. It’s a general question, not a specific problem. No other info needed.
You rejected the use of satellite trajectory data.

For any problem you want to solve, you have information you know and an answer you want to find. The information you know may or may not be sufficient to find the answer.

You've told us what you want to find, but nothing at all about what you know, so someone made a guess. And you responded, no, we don't know that.

I can think of several other methods requiring different known data. If I post them, will you tell me that, no, we don't have that information either? Why don't you save us the time and give us more of the constraints that you aren't telling us.

Or, if the basic constraint is that we know nothing then the answer is easy: we can't find g.
 
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You’re a staff mentor? Dude. You have a terrible disposition. I didn’t reject satellites. I merely asked what if there are none, to draw out more responses. Where did I respond “no we don’t know that”? If you can think of several other methods that require different known data then list them because that’s exactly what I want to know. If you can’t do that just move along.
 
  • #13
JD Duncan said:
If you can think of several other methods that require different known data then list them because that’s exactly what I want to know.
Drop something and measure its acceleration.
 
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  • #14
JD Duncan said:
You’re a staff mentor? Dude. You have a terrible disposition.

And you're awfully demanding when it comes to free help.

Ibix is 100% right. It is far easier to measure GM than G, and GM gives you g vs. r. Russ is 100% right. If you don't have anything you can see move in the gravitational field you have no way to measure it.
 
  • #15
How in the world have I been demanding? Point to one phrase where I have demanded anything.
 
  • #16
The problem is that you are asking an incredibly open question. The simple answers are to look at orbits (dropping something is a subset of this) or weigh something of known mass. But we could go on spinning out wilder and wilder ways of measuring ##g## in ever more complex ways probably forever.

So although V50 and Russ are being blunter than I would be, they are asking the next question I would ask: why do you want to know? I very much doubt that an exhaustive list of possible experimental methods could ever be written. The obvious ones are above.
 
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  • #17
Thanks for your reply, Ibix. I wasn’t looking for any wild manifestations of the task. Just simply if anyone new another way. Perhaps it’s too simple a question for the cerebrally afflicted, and before anyone jumps on me again, that’s a compliment. You’re the first to ask why, so I’ll answer. I’ve found a way to calculate any body’s gravity (the acceleration variety) independent of the gravitational constant and just wanted to make sure it is unique before submission for print.
 
  • #18
JD Duncan said:
I’ve found a way to calculate any body’s gravity (the acceleration variety) independent of the gravitational constant and just wanted to make sure it is unique before submission for print.

PF is not for discussion of personal speculations or original research.

Thread closed.
 

1. What is the difference between little g and big G in solving for gravity without gravitational constant?

Little g (g) refers to the acceleration due to gravity at a specific location on Earth's surface, while big G (G) is the universal gravitational constant that is used in the equation for Newton's law of gravitation. In solving for gravity without gravitational constant, we use g instead of G to account for the variation in gravity at different locations on Earth.

2. How is little g calculated for different locations on Earth?

Little g can be calculated using the formula g = GM/R^2, where G is the universal gravitational constant, M is the mass of Earth, and R is the distance from the center of Earth to the location. This formula takes into account the variation in Earth's mass and radius at different locations.

3. Can we use little g to solve for gravity on other planets?

Yes, we can use little g to solve for gravity on other planets. However, the value of g will be different on each planet due to differences in mass and radius. The formula for calculating g remains the same, but the values for M and R will be specific to the planet in question.

4. Why is it important to solve for gravity without gravitational constant?

Solving for gravity without gravitational constant allows us to account for the variation in gravity at different locations on Earth. This is important in fields such as geology, where the strength of gravity can affect the behavior of materials and structures. It also allows for more accurate calculations in fields such as space exploration and satellite technology.

5. Are there any limitations to using little g in solving for gravity?

While using little g can provide more accurate calculations for gravity on Earth, it does have limitations. The formula for calculating g assumes a spherical Earth with uniform density, which is not entirely accurate. Additionally, it does not take into account other factors that can affect gravity, such as topography and atmospheric conditions. Therefore, it is important to use g with caution and consider other factors when necessary.

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