There is an excellent site ScienceNet where you can find out about gravity (or indeed any other vaguely scientific query) The great thing is that if you are in the UK you can phone them up for free and ask the experts about pretty much anything scientific, or ask for clarification on anything you don't understand.
If it's too obscure for them to give an immediate answer, they'll either phone or email back (your choice) when they're found the answer. I've found them to be always wonderfully helpful.
Ed