Before you start setting up your award winning science fair concept, be sure you know the difference between a demonstration and a science experiment.
A SCIENCE DEMONSTRATION is a quick little science "show" that explains a science concept like building a model volcano and watching it erupt. It shows how something works, but it is not a true experiment.
A SCIENCE EXPERIMENT is usually more involved and in most real experiments you compare results. An example would be "What fertilizer works best on plants?" or "What is the strongest brand of paper towel?" In these examples, you ask a question and then perform experiments to get the answer.
Hopefully that makes sense. Most science fairs are looking for experiments, not just demonstrations, but check with your teacher to be sure before you get underway.