gravity

asher: mom? if the earth is a round circle, then how do we stay up straight on it?
me: uhhhh, well, when God made the earth he made a natural force called gravity to go along with it. the law of gravity says that whatever goes up must come down. does a ball stay floating in the air when you throw it up?
asher: nope.
me: that's because gravity makes it come back down. it holds us to the earth.
asher: sooo, you mean that God made gravity, which is like a big vacuum in the earth that sucks us down.
me: yeah, kind of like that.

we were just riding along in the car and out of nowhere he asks the above question. i have no idea how to explain the law of gravity to a 4 year old. heck, i don't even really understand it myself!