NEED HELP FOR SCIENCE FAIR PROJECT!!!?

So I have a science fair coming up and I need to think of a project. Even though im only in 7th grade, I go to a private school and we are expected to do the very best that we can. I need something that is not hard but not too easy... it also needs to have and if then statement such as "if u jump, then you will land on the ground". there can be no simple yes/no answer. I have to be able to measure and record data. And I also have to be able to use the scientific method. I know that this is a lot to ask but i will be extremely grateful for an answer. thanks in advance