1) Make a wooden door and frame and connect them with metal hinges. Paint it blue. When asked what scientific concept it demonstrates, open the door and say "it demonstrates forces" then slam it shut and say "it also demonstrates inertia".
2) Stand still and wave your arms around. When asked what scientific concept it demonstrates, say "my body is moving through time, but my arms are moving through space AND time."
Sciencebuddies.com has some interesting science fair ideas that are reasonably priced. You may also want to look at ehow.com.
There are many science ideas to be found online. Sites such as Science Buddies, Kidz World, Cool Science Projects, and even Brown University feature dozens of science fair ideas for multiple abilities and grade levels.
i dont no i was hopin you would tell me...
eating your butt
For a middle school aged child, you can find some excellent science fair solar system projects online. A great site to look for ideas is sciencebuddies.org. Look under the "Project Ideas" tab on that website.
1. Momentum of a horse.
Solar powered car, wind car.ect.
you could make a generator that when turned either a. lights up the light at the end of the sonic screwdriver or b. lights up the TARDIS light.
why are dolphins dying off
One of the most popular science fair project and one you see on television shows everywhere is the volcano made from baking soda and vinegar. Some more fresh and not so used ideas include the molding process of bread and the science behind growing crystals.
Volcanoes, Hatching Eggs, Spaceships, and I like the candy or tornado tests
Maybe a broom that can fly using hoverboard techniques?