The Naked Scientists Forum

Author Topic: G formula is wrong  (Read 1680 times)

nic

• First timers
• Posts: 5
G formula is wrong
« on: 24/04/2012 10:32:38 »
also i think the G formula is wrong,because it`s used for variables calculation which are already estimated with G...
for example,we calculate firstly distance between sun and earth and then earth and sun masses...
all planets are supposed to have a mass and radius,but nothing it`s said about their move,although `radius` is because of spinning(implicit)...

simplified

• Sr. Member
• Posts: 428
Re: G formula is wrong
« Reply #1 on: 24/04/2012 14:27:30 »
also i think the G formula is wrong,because it`s used for variables calculation which are already estimated with G...
for example,we calculate firstly distance between sun and earth and then earth and sun masses...
all planets are supposed to have a mass and radius,but nothing it`s said about their move,although `radius` is because of spinning(implicit)...
Even if G is wrong then it still is useful.Your denying of G still is useless. ;)

nic

• First timers
• Posts: 5
Re: G formula is wrong
« Reply #2 on: 24/04/2012 15:08:16 »
i prefer to say that i don`t know instead of calculating nonsense...

Phractality

• Hero Member
• Posts: 523
• Thanked: 1 times
Re: G formula is wrong
« Reply #3 on: 24/04/2012 21:23:05 »
We know the value of G to a fair degree of accuracy. According to Wikipedia,
Quote
"Assuming SI units, F is measured in newtons (N), m1 and m2 in kilograms (kg), r in meters (m), and the constant G is approximately equal to 6.674×10−11 N m2 kg−2."

Here is one method we use to measure it.

I think the best way to measure G would be to put a pair of reference masses into solar orbit away from any other orbiting bodies. Each of the two reference masses should have a retro-reflective target. A third satellite (small enough and far enough so its gravity doesn't have a significant effect on the reference masses) should have a laser range finder to measure the orbital parameters of the two reference masses. Once you know the exact orbital parameters of the system, you can calculate G from Kepler's third law. The accuracy of the measurement depends on the accuracy with which you know the masses and measure the orbital parameters. I expect that this could be done to at least ten significant digits.

If each of the reference masses is exactly 1,000 kg, and the semimajor axis of the orbit is exactly 100 m, the orbital period should be about 107,000 hours (12 years). For the same masses 10 m apart, the period would be about 140 days. (I'm having trouble finding the right Kepler's 3rd law calculator. Someone please check my figures.) Optimizing the masses and distances to get the best accuracy for minimum cost will take some serious thinking.

Ęthelwulf

• Sr. Member
• Posts: 358
Re: G formula is wrong
« Reply #4 on: 24/04/2012 21:28:18 »
Maybe you should define G for him, without all the numbers. To laymans, numbers mean nothing only explanations.

nic

• First timers
• Posts: 5
Re: G formula is wrong
« Reply #5 on: 25/04/2012 07:40:19 »
`I think the best way to measure G would be to put a pair of reference masses into solar orbit away from any other orbiting bodies. Each of the two reference masses should have a retro-reflective target.`
you think,but you never did or will...because you cannot do it...and never will know the answer...
« Last Edit: 25/04/2012 07:41:58 by nic »

Phractality

• Hero Member
• Posts: 523
• Thanked: 1 times
Re: G formula is wrong
« Reply #6 on: 25/04/2012 21:50:11 »
`I think the best way to measure G would be to put a pair of reference masses into solar orbit away from any other orbiting bodies. Each of the two reference masses should have a retro-reflective target.`
you think,but you never did or will...because you cannot do it...and never will know the answer...
No; I personally won't do it because I don't have a billion dollars in my pocket. NASA could do it, and they could determine G to a much higher precision than what we have now. It's just a question of priorities.

The value of G is not fixed by definition; it has to be measured by experiment. Experiments have been done, and they are not, as you suggest based on circular logic. The experiments that measure G are based on the definitions of meter, second and the speed of light. The value of G determined by those experiments is then used to determine the mass of Earth, sun and planets. We don't turn that around and use the mass of Earth and sun to calculate G.

The Naked Scientists Forum

Re: G formula is wrong
« Reply #6 on: 25/04/2012 21:50:11 »