How can I win the science fair?

Ohmygosh I'm starting science fair and I was wondering if anyone has any good ideas out there? I want a really interesting one that could win. because I really really want to win. I've dont science fair for 2 years and the best I've done is 3rd place. And I'm striving for first. Please tell me any interesting topics. I've been surfing the net for hours but most of them you have to buy and whatnot. I just want a good idea. Thanks.

this girl in my seventh grade class did something on how water takes up more space then alchoal...like you have a cup of water and a cup of rubbing alchoal..and you can pour the cup of alchoal in the cup of water without it overflowing because the alchoal molequels like fit inbetween the water molecules...

this was like 6 years ago

so I might not remember how it went

it was really cool though and I still remember it 6 years later

hey thanks. I'll look it up. if anyone else has any ideas, please tell me.