How can I convince my dad to let us get a trampoline?

Maybe promise to help out around the house in exchange for him getting it? Also explain what you've told us how it would keep you active and promise to be careful. Word to the wise though, if you get it, tie it down real good, maybe in cement. We had one and a freak thunderstorm blew ours over the fence and into the road, ruining it. I live in the Texas panhandle though, some of the worst wind around, where you live might be different.