# What is Gravitational constant: Definition and 84 Discussions

The gravitational constant (also known as the universal gravitational constant, the Newtonian constant of gravitation, or the Cavendish gravitational constant), denoted by the letter G, is an empirical physical constant involved in the calculation of gravitational effects in Sir Isaac Newton's law of universal gravitation and in Albert Einstein's general theory of relativity.
In Newton's law, it is the proportionality constant connecting the gravitational force between two bodies with the product of their masses and the inverse square of their distance. In the Einstein field equations, it quantifies the relation between the geometry of spacetime and the energy–momentum tensor (also referred to as the stress–energy tensor).
The measured value of the constant is known with some certainty to four significant digits. In SI units, its value is approximately 6.674×10−11 m3⋅kg−1⋅s−2.The modern notation of Newton's law involving G was introduced in the 1890s by C. V. Boys. The first implicit measurement with an accuracy within about 1% is attributed to Henry Cavendish in a 1798 experiment.

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1. ### B Why exactly do we need the gravitational constant?

That may seem like a silly question, but suppose the crew of an interstellar vessel wanted to measure the mass of their ship, perhaps to estimate remaining resources. Unless they have very well calibrated thrust and a very well calibrated accelerometer, the only option is to do so...
2. ### A The gravitational constant measured by the smallest object

In https://physicsworld.com/a/physicists-measure-smallest-gravitational-field-yet/ the gravitational constant was measured by the smallest object until now, this is a small golden ball, with a radius of one mm. The intention is to measure some quantum gravitational effects in the future. But, I...
3. ### I The Non Constant Gravitational Constant (G)?

History & evidence can be found in: https://onlinelibrary.wiley.com/doi/full/10.1002/andp.201900013 https://phys.org/news/2015-04-gravitational-constant-vary.html {unacceptable reference deleted} The experimental data strongly suggest are actual x,y,z,t variations in the measured value of G
4. ### What is the reason that the Gravitational Constant (G) varies?

If G really not a constant then what are the implications in science?
5. ### Java Changing the Universal Gravitational Constant: A Java Applet

Hello folks, I am working on Java program just for fun to model an n-body problem using 3-dimension graphics. I'm looking for a way to speed up the model. Suppose for example that I decide to increase the speeds of all objects by a factor of, say, 2. To compensate, I would also increase the...
6. ### B Cavendish experiment help for a dummy please

Hey Yas. I have the materials to perform a Cavendish Experiment. I understand the concepts, I understand what is being measured but I am a mathematics idiot. What I request is someone to to just show me the equation and how to operate it in the simplest of terms. ie put the radius of the...
7. ### MHB Need help with reversal of a calculation involving gravitational constant.

Hi. I would like to know if it is possible to "reverse engineer" the formula below to find (G) if Ve, M and r are all known values. Ve = sqrt{2GM/r} Ve would be escape velocity, G would be gravitational constant, M would be mass of planet and r would be radius of planet. I hope I am...
8. G

### Is gravitational constant unchanging over age of universe?

do we know for a fact that the gravitational constant has always been the same since the dawn of the universe? I feel like gravitational forces should slowly be decreasing as the universe ages (meaning that assuming mass of Earth doesn't change, we should weigh a bit less in a billion years)...
9. J

### Determine the direction and acceleration of the bead

Homework Statement Three lead spheres, of mass 10.0 kg each, are located at three corners of a square of ice length 45.0 cm, as shown. A bead is released at the forth corner. By considering the gravitational forces among the four objects only, determine the magnitude and direction of the...
10. ### I Lorentz transformation of the Gravitational constant

Since force is transformed via: F'x= Fx ; F'y= Fy/ ϒ; F'z=Fz/ ϒ (F' is the force related to the moving frame, F is the force on the rest frame and ϒ=1/√1-v2/c2 ).I expect that G (Gravitational constant) will be transformed between moving and rest frame in order to satisfy force transformation...
11. ### How Fast is an Asteroid Traveling Toward Earth?

Homework Statement A asteroid is hurtling towards Earth and humankind has decided to fire a nuclear warhead at it in order to avert disaster. In order be most effective the rocket carrying the warhead has to impact the asteroid at 40km/s. The rocket itself travels at 12km/s. What remains is to...
12. ### B Deriving the gravitational constant factor for lbf

I have never had to use the English Engineering System so I am having a bit of a struggle here. I understand the concept of an inconsistent system of units. I understand the following 2 statements: 1lbf = 1lbm x 32 ft/sec^2 1lbf = 1slug x 1 ft/sec^2 When given a problem that is asking for the...
13. ### A Progress in measurement of gravitational constant?

I read that in 2014 the gravitational constant was measured by atomic intereferometry. Now I read that they speculate that measurements of G are in correlation with 5,9 years cycle. But, when we can expect new measurements of G? Are they in preparation?
14. ### I Gravitational Constant in GR: How & Why?

(precursor: I have not formally studied GR) I have noticed that the gravitational constant found in classical gravitation is also used in GR. Why is this the case? Am I correct in thinking that the constant was determined by Cavendish and was for the classical theory of gravitation? So, my...
15. ### I Gravitational constant for normalized masses

hi, i'm totally confused right now. I'm playing around with a simple orbital model of the sun and the earth. since my rigid body solver doesn't like the huge masses of those bodies, i just normalized the masses to those of the sun. so i have m_sun = 1 and m_earth=3.0044e-6 as dimensionless...
16. ### A Force Question – Einstein Gravitational Constant

The Einstein gravitational constant (Κ) is usually written as; Κ = 8πG/c4 Can this constant be represented as wave-particle ratios of force? One ratio is a thermal ratio, it includes Plank temperature and Hawking temperature. The other ratio is a particle ratio including Plank mass. Can...
17. ### I Dark energy and the gravitational constant

Many have claimed that if dark energy was not so small then the universe would fly apart and we wouldn't be here. However what if you increased the value of lambda and at the same increased the value of the gravitational constant ( or perhaps the amount of matter or dark matter in the universe)...
18. ### Determining universal gravitational constant G

Homework Statement Choose two masses and vary their separation, measuring the force between them each time. Plot a straight line graph and use the gradient to estimate the universal gravitational constant. Include uncertainties in the results and express values with the appropriate number of...
19. ### Help with a Universal Gravitational Constant

I am doing an Astronomy GCSE. I have to work out the orbital period for a satellite. I have got quite far with it, but I am really stuck. I have spent hours at it! This is the question:- A space laboratory is in circular orbit around the Earth at a distance of 6000km from the Earth's centre; its...
20. ### Possible to derive an approximation of G from a Saros ?

I recently read a paper titled : " The Saros cycle: obtaining eclipse periodicity from Newton's laws " My question is, more or less: " Is it possible to obtain an approximation of G by observing Saros periodicity ? " I'm currently studying the derivations of the Lunar , Solar, and Stellar...
21. ### Gravitational Constant: Why Is It Fundamental?

Hi, I was wondering if there is any need in the theory of relativity for Newton's Gravitational Constant 'G' to remain a fundamental constant. Constant in Coulomb's Law can be expressed in 'c' and 'pi', then why Constant in Newton's Law needs to be a fundamental constant??
22. ### Gravitational Constant and Velocity

Homework Statement Jupiter's moon Io has active volcanoes (in fact, it is the most volcanically active body in the solar system) that eject material as high as 300 km (or even higher) above the surface. Io has a mass of 8.94 × 1022 kg and a radius of 1815 km . Ignore any variation in gravity...
23. ### Speed of light depending on gravitational constant?

I just wonder if there were any serious (and peer reviewed published, to be in line with guidelines) theory, which had proposed some link between speed of light in vacuum constant and between gravitational constant G. For example a calculation of speed of light based on G. Tried google search...
24. ### Have we derived the Gravitational constant via General Rel?

My friend and I were discussing this, and google didn't seem to reveal any result. Much like how Bohr's theory managed to derive the Rydberg constant without much effort, has the gravitational constant been found in terms of other quantities yet? It just seems bizarre that Newton proposed a...
25. ### Dirac theory over gravitational constant reduction.

Dirac had proposed that Gravitational constant would reduce with time.Why?
26. ### Is 1/4π built into G, the gravitational constant?

We went over Coulomb's law today, which can be stated as (1/ε0)(1/(4πr2))(|q1q2|) This equation is very similar to Newton's law of gravitation, but it contains 1/4pir^2. This makes sense, because the electric force is being diluted over the surface of a sphere. Is 1/(4πr2) built into G as well?
27. ### Is the gravitational constant actually a variable?

Hi, as an engineer i don't have much formal training in theoretical physics so bare with me. As most of you know, we can only understand 4% of our universe with the current models we have. The rest of the 96% is dark matter and dark energy (23% and 73%, respectively). Could these unexplained...
28. ### How did Newton discover universal gravitational constant?

I'm curious as to what he did to figure it out *Newton, sorry
29. ### Gravitational Constant: Earth vs Other Planets

Quick question... Can the gravitational constant only be used for Earth or can it be used in questions regarding other planets?
30. ### What if the Gravitational Constant were larger?

In our dimensions, it is ~6.67384 × 10-11 m3 kg-1 s-2. I recall having read a Hawking article a long time ago in which the ideas of greater or smaller variations of this constant were toyed with, and what they would mean for their respective universes (with other constants unchanged from the...
31. ### Precision of the values of gravitational constant G

Homework Statement What are the magnitud of G (gravitational constant) and the age of the solar system in CGS system of units and in seconds respectively? and what is the precision of these values and why? Homework Equations The Attempt at a Solution I found that the value of G in CGS system is...
32. ### Gravitational constant in english units

Hello, I am taking a fluid mechanics class right now, so I deal a lot with water flowing through a pipe, and equations involving the density of the fluid. The problem is, that since I'm an engineering major, we use way too many english units. There is something inherent about non-SI units I...
33. ### The universal gravitational constant (G)

A most common tool in engineering is "Dimensional Analysis": http://en.wikipedia.org/wiki/Dimensional_analysis This tool can provide you with the dependence and scale. For example, using Dimensional analysis one can easily derive how the Period of a pendulum, T, is dependent on string length...
34. ### Gravitational constant problem

Homework Statement Titania, the largest moon of the planet Uranus, has 1/8 the radius of the Earth and 1/1700 the mass of the earth. a) What is the acceleration due to gravity at the surface of Titania? b) What is the average density of Titania? Homework Equations F_{g} =...
35. ### Is Gravity Merely a Byproduct of Electromagnetic Forces?

Hello, I am vexed by the Gravitational constant G. I have always thought that the gravitational force is proportional to mass and inversely proportional to distance^2, but it seems that it cannot be as cut-and-dry as this if we need to scale the relationship by G, with units of...
36. ### Gravitational Constant (Big G I think)

G = (6.674215 ± 0.000092) x 10-11 m3/kg/s2 or there abouts is the constant that we multiply to the mass of m1 to m2 divided by the distance squared. This gives us the attractive force between bodies. In the equation F = G(m1m2/r2) it is obvious that the attractive force depends on the mass of...
37. ### Constancy of gravitational constant

Hello, We are being taught about coulomb's law, my teacher said that the constant in the law which we denoted by k, changes with change in medium because of permittivity of the medium. But why does the constant changes unlike the gravitational constant which does not change with medium...
38. ### Gravitational Constant: Questions and Ideas

Hey, I have got some guestions, when I philosophized with me friends... We have classic gravitational constant, say G... And now, constant is 2G, 5G or 100G... (increases). Others constants and physics legislation is normal. THEREAFTER... How is live on Earth? And other planets and...
39. ### Gravitational Constant Measurement ?

How did we measure the gravitational constant G = 2.034 x 10 ^ 17 cm ^ 2 and the Earth average density (specific gravity) p = 3.45 g / cm ^ 2 s ^ 2.
40. ### What is Newton's gravitational constant mean?

As the title already suggests, what does Newton's gravitational constant mean, and what it is, and how it is used in our universe? Hope you can help.
41. ### Help Solving Gravitational Constant Equation

Hi, I was just hoping for some help in explaining the steps to solving an equation using the universal gravitational constant. I can easily find the answer online but not easily find out how to actually solve it, since I want to understand what I am doing. I understand the basics of equation...
42. ### Need help with Gravitational Constant (G)

With this formula, you should apparently be able to work out the schwarzschild radius with 2GM over c^2 but it shows the gravitational constant on google being: G = 6.67300 × 10-11 m3 kg-1 s-2 Can someone please explain this to me? - Because then I would be able to work out the...
43. ### Universal gravitational constant

hey, so in Newtons equations for gravitational force etc, the constant 'G' is used. where does that come from? how do we know it's value? how was it discovered? thanks, Lntz
44. ### Understanding the Gravitational Constant Formula | Jamie

Can someone explain the following formula to me? I would like to know what m, kg, and s are. At glance I believe this is the cross product of 6.67384 and the other half of the formula. However I am very unsure on how to continue into solving this for any specific value. I believe m is for the...
45. ### What is the meaning of m3 kg-1 s-2 in gravitational constant

what is the meaning of m3 kg-1 s-2 in gravitational constant
46. ### Java Gravitational Constant Problem in Planetary Java Model.

Hi there I am currently trying to implement Newtons law of gravitation into a planetary model. I have 2 objects with mass of 500 and 20. The distance between them is 150. From what I gather from wikipedia I could use the following formula: GravityField = G * ((500*20)/(150^2)) Where G...
47. ### Universal Gravitational Constant

I was wondering if somebody could please explain the gravitational constant to me and also if they could give me the correct equation for it and explain the equation, because I have been receiving many odd variations of the gravitational constant and I would really like a good clear explanation...
48. ### Calculating Gravitational Acceleration at a Planet's Surface

Homework Statement http://img26.imageshack.us/i/1113001.jpg/ #13 Homework Equations m=F/a F=g(m1m2)/r^2 The Attempt at a Solution well, the answer is D, but I am not sure how a planet's size can affect an object's weight on there. I am guessing you have to use the...
49. ### The Universal Gravitational Constant G

Does it apply to planets other than Earth? I'm just learning (cramming) this stuff; sorry if it's a dumb question.
50. ### How to calculate gravitational constant

I don't seem to understand the m3 km and seconds used in the gravitational constant. If one body weighed 100kg and another 75kg could someone show me step by step how to solve this? I am 13 so please try to explain it at this level. Thanks.