# Recent measure of G constant

1. Jun 23, 2015

### Tony Stark

Has there been any recent changes in the G constant value?

2. Jun 23, 2015

### Tony Stark

I meant in the official value of G known to us?

3. Jun 23, 2015

### SteamKing

Staff Emeritus
Since G must be determined experimentally, there will be some variability in its reported value.

This article, Ref. 9, contains a report on the latest measurements of G:

https://en.wikipedia.org/wiki/Gravitational_constant

4. Jun 23, 2015

### D H

Staff Emeritus
The job of the CODATA Task Group on Fundamental Constants is "to periodically provide the scientific and technological communities with a self-consistent set of internationally recommended values of the basic constants and conversion factors of physics and chemistry based on all of the relevant data available at a given point in time."

Updates are released every four years. This update will be published online at http://physics.nist.gov/cuu/Constants, supposedly in May or June 2015, but that hasn't happened yet. That site still has the CODATA 2010 values. It's still June 2015, so nominally this should any day now -- or maybe not.

5. Jun 23, 2015

### rootone

G cannot be a constant since the mass of the Earth is not a constant.
In fact several tonnes of micrometoric dust is accumulated every day.
Although that makes no significant difference to the measure of G over the course of a human life time, it might make a difference on geologic time scales.

6. Jun 23, 2015

### SteamKing

Staff Emeritus
This just means that GMearth varies slightly over time.

The variation in G over longer time scales has been studied using astronomical phenomena:
from the Wiki article linked above.

7. Jun 23, 2015

### D H

Staff Emeritus
You are confusing G, the Newtonian gravitational constant, with g, gravitational acceleration at the surface of the Earth. Big G is dimensional physical constant, the G in $F=\frac {Gm_1m_2}{r^2}$ (Newton's law of gravitation). That is modern notation; Newton himself didn't express his law of gravitation that way, nor did Henry Cavendish, the first to measure G (but only after the fact). Cavendish intent was to "weigh the Earth".

Measuring G is extremely non-trivial. It is the least well known fundamental physical constant.