# Dimensional analysis to estimate gas clounds collapse

1. Sep 11, 2010

### leonne

1. The problem statement, all variables and given/known data
stars form by gravitational collapse of interstellar gas clouds. use dimensional analysis to estimate how long it takes for a cloud with a density p=Mo pc^-3 to collapse

Mo= 1.9898e33 g
2. Relevant equations

3. The attempt at a solution
I just have no idea how to use dimensional analysis, and how I would use it to solve the problem. My book has nothing about it. So if someone can explain to me how I use dimensional analysis step by step solve this problem.

Thanks

2. Sep 12, 2010

### leonne

Hey
after reading I have better idea on what to do. Here is what i got.

PgML/po I have to try to get the signs to cancle out and just to be left with time right?

so P= ML-3 for density g= M-1 L3 T-2 for gravity. po = MLT-1 for momentum so all of the cancel and you are left with time. Is that the right formula? Hmmm but how am i suppose to find how long it will take without the mass length or momentum? or did i do something wrong?