In most cases, the subject of the project will be completely up to you. This may seem scary, but actually this is where the fun comes in. When your teacher assigned a science fair project, he or she gave you the freedom to come up with a project idea that would be interesting to YOU. Instead of a normal homework assignment that's designed by your teacher and given to you whether you want it or not, the science project is invented by you, so you can explore things that interest you the most. It's a unique opportunity that allows you to learn while also expressing your creativity, both in the design of the experiment and the project display that will eventually be shown at your science fair.