When it comes time for the science fair I notice several displays that are not a science experiment, but are a demonstration instead. What is the difference? The scientific method is the difference. In order to be an experiment there is something that is being tested by the scientist. If nothing is being tested it is just a demonstration.
The hypothesis is the test phrased as a statement. For example "Baking soda and vinegar have a reaction when mixed. I think the vinegar has more control over the reaction then the baking soda." To actually run the example experiment the scientist will need at least three samples with the same amount of baking soda in each. The only difference will be the amount of vinegar used.
When the time comes for science fair remember experiment not demonstration.