# Gravitation constant, G

1. Dec 26, 2008

### DrChem

gravitation constant has been determined experimentally by cavendish. Its value has been found to be always a constant. The expression for G is given as G=Fd*d/Mm. I would like to know-
on what factors does gravitation constant depend?

2. Dec 26, 2008

### Staff: Mentor

Hi DrChem, welcome to PF!

I don't understand your question. Something which is constant, by definition, does not depend on any factors.

3. Dec 26, 2008

### Math Jeans

I concur. The gravitational constant simply defines to what magnitude mass effects the gravitational force.

By "factors", do you mean to ask how natures form of creating gravity has the specific magnitude of the gravitational constant? Unfortunately, no one really knows.

4. Dec 27, 2008

### DrChem

if a value is determined experimentally will that not mean that it depends on those terms which were responsible for its determination.
does this mean that any constant is independent of any factor.

5. Dec 27, 2008

### Nick89

The value is not determined experimentally, it is only approximated by measuring it. We don't (and probably never will) know the exact value of G.

Just like you can measure your mass (or weight). Your mass does have an exact value, but you will never know it exactly, you can only measure it and determine an approximate value for it.

6. Dec 27, 2008

### Staff: Mentor

No. For example, consider determining the resistance of an ideal resistor. In order to determine its resistance we must apply a voltage across it and measure the current. Then we can take the ratio of the voltage over the current and we have the experimentally measured resistance. We can apply a different voltage, measure the new current, and get the same ratio. Despite the fact that you need to apply a voltage in order to experimentally determine the resistance we still say that the resistance does not depend on the voltage because we can apply any voltage and measure the same value for resistance.

Mathematically V=IR defines resistance and says that we need a voltage and a current in order to measure resistance. In contrast, dR/dV=0 says that the resistance is constant (wrt V) and therefore its value does not depend on the voltage. Does that help?

Yes, again, that is the definition of the word "constant".

Last edited: Dec 27, 2008
7. Dec 27, 2008

thank u