Question

What should I do for science fair

Answer 1

Don't do a volcano at the same time you want to be creative and I personally feel that a volcano is too cliché.

Answer 2

You could Build a  Gumdrop Geodesic Dome !

Geodesic domes are approximately sphere-like structures made up of interconnected triangles. A famous geodesic dome is Spaceship Earth at EPCOT in Walt Disney World, Florida, but geodesic domes are also commonly found as climbing domes at playgrounds. In this science activity, you will get to build a simple geodesic dome using gumdrops and toothpicks. Once it is built, you may be surprised by how strong it is! Get ready to do some tasty engineering!

 Materials:
Gumdrops (11). Alternatively, jelly beans or other semi-firm, chewy candies may be used. Toothpicks (25)
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Instructions:

1.Attach five toothpicks together using the gumdrops to form a flat pentagon (five-pointed) shape. You should have a gumdrop at each point and a toothpick along each edge.
2.Poke two more toothpicks into each gumdrop, arranging the new toothpicks so that they are pointing up.
3.Take five new gumdrops and attach them to the top of the new toothpicks, putting two toothpicks into each gumdrop, to form triangles. (The pentagon should form the base of the triangle, and the new gumdrops should form the top point.) You should end up with five triangles this way.
4.Attach a toothpick between the top points of the triangles you just made, connecting the triangles together. This uses five toothpicks, and will create another pentagon shape, this time at the top of the dome.
5.Take five more toothpicks and poke one into each of the five gumdrops that make up the top pentagon. Arrange the new toothpicks so that they are pointing up. Then poke all five toothpicks into a gumdrop in the middle, and at the top, of the dome. Your geodesic dome is complete!
6.Gently press down on the top of your geodesic dome. If it does not break, try carefully pressing down on it a little more.