Modeling grass

Hi everyone.
I’m using Blender (newest stable version 2.63a)
Possibly is a banal question, but I searched across the forum and I haven’t found an answer.

first: When modeling grass, it is preferable from many particles (hair, of course) or use the “child”?. In other words. It’s better use 10.000 hair or use 1.000 and 10 child?

second: Can I use “collision” avoiding the grass does not come through other elements? or I need to use other trick (imagine: a person sitting on the grass)

Sorry, English is not my mother tongue
best Regards

I’m new to Hair particle system. But as I experienced, it’s better to use 10.000 hair and 10 child. 1.000 + 10 child has different results with 10.000 although it has the same amount. If you adjust it to 1.000 + 10 child, the result is 1 hair (or grass) is surrounded with 10 grass, so the total is 10.000 particle. If you use 10.000 particle with no children, so the result is the emitter just produce 10.000 particle without another particle surrounding it.

I think that explaining this is difficult by words, so sorry if my sentence pattern is messy.

Dear “220696”
Tnx for a quick response…
I was using 1.000 + 10 child rather than 10.000 'cause I thought it’s was using less vertex (in other words, less memory or slow process).
For the second questions, (a person sitting in the grass, for ex) I use a “short hair” to avoid the hair to pass trrough the legs, foot or any element. Even “combing” the hair…but I suspect that there must be another solution. I tried to use “collision” with the body of this person but…
So, in brief: I need to have a manual of blender 2.63? (even another version)
Unfortunately, the english isn’t my mother tonge and all the tutorial’s author speaks so quick…