Pretty good resource for that kind of thing if you have another interested kid and access to the internet. There's also this:
https://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation
Pretty good resource for that kind of thing if you have another interested kid and access to the internet. There's also this:
https://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation