# Homework Help: The base units of the Gravitational Constant 'G'?

1. Mar 31, 2005

### rindishy123

Hi.

Part of my homework was to work out what the SI base units of the gravitaional constant are.

I'm crap at working out base units so could somebody help me out?

Thanks

If anyones wondering, G is 6.67 x 10ˉ¹¹ N m² kgˉ²

2. Mar 31, 2005

### whozum

m and kg are base units, what are the base units of a newton?

3. Mar 31, 2005

### dextercioby

Yes,also "s" is the unit that enters "G"...Incidentally,in any system of units,SI-mKgs included...

Daniel.

4. Mar 31, 2005

### rindishy123

i think i worked it out...

could anyone clarify if the correct base units are :

kg m² sˉ²

5. Mar 31, 2005

### Nylex

That's not right. What are the base units of a newton, again?

6. Mar 31, 2005

### whozum

No, you are missing something. Try this:

$$N x m^2 x kg^{-2}$$

If you can find the units of a newton in base units, just plug it into the above expression and simplify to get the base units of G.

7. Mar 31, 2005

### rindishy123

units of a newton are m kg s-2

8. Mar 31, 2005

### dextercioby

Okay.What about the fraction in the RHS of Newton's gravity law...?

Daniel.

9. Mar 31, 2005

### Nylex

Yep, so how did you come up with your answer for the base units of G? .

10. Mar 31, 2005

### rindishy123

i dont knoww!!!!! i mentioned i was **** at doing these things in my first post!!!!

somebody please just tell me how to do it! this is in for tmoro!

11. Mar 31, 2005

### Nylex

You have the base units of a newton and the rest of your units for G are base units. As whozum said, just plug your base units for a newton into your collection of units for G..

12. Mar 31, 2005

### whozum

$$kg * m * s^{-2} * m^2 * kg^{-2}$$

Making it easier for ya :)

13. Mar 31, 2005

### chroot

Staff Emeritus
It's just a fraction, rindishy:

$$N \cdot \frac{m^2}{kg^2} = \frac{kg \cdot m}{s^2} \cdot \frac{m^2}{kg^2} = ...$$

Cancel the redundant units, and you're done.

- Warren

14. Mar 31, 2005

### rindishy123

ohh

so:

m3 kg s-2???

and how do you make those lovely italic expressions? :)

15. Mar 31, 2005

### dextercioby

Not really.

$$m^{3}(Kg)^{-1}s^{-2}$$...

Using Latex.

Daniel.

16. Mar 31, 2005

### rindishy123

ok im off back to grade school