# Question about the constant.

1. Jan 29, 2009

### NewDescartes

I was wondering where the Gravitational Constant comes from. As far as I know it has been measured with a tension line and weights. I also understand that Newton uses it his gravitational formula, but he didn't measure it. Did he just guess the number? Also is G the proportionality or distribution of gravity per kg?

2. Jan 29, 2009

### atyy

3. Jan 29, 2009

### JesseM

As for the other part of NewDescartes' question, it says here that Newton couldn't actually establish any good estimate for the value of the gravitational constant (and it says here that when calculating things like planetary orbits, Newton used equations 'with ratios so that the constant would cancel out'). So, the Cavendish experiment really was the first to give it a value.

4. Jan 30, 2009

### NewDescartes

So the gravitational constant is approx. 6.67428 * 10^11 newtons??

5. Jan 30, 2009

### NewDescartes

By the way thanks for everything. I enjoy this immensely, even debates.

6. Jan 30, 2009

### Staff: Mentor

To be picky, the units are newton m^2 / kg^2.

7. Jan 30, 2009

### buffordboy23

Don't forget the minus sign in the exponent.

According to the Constants section of PF's Latex Reference,

$$G\ =\ 6.673(10)\ \times\ 10^{-11}\ m^{3} kg^{-1} s^{-2}$$

I prefer the units representation given by jtbell much more though.

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