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University of Liverpool: Matter Initiative for Schools a Level Resources
This site features numerous interactive resources (such as simulations, interactive exercises, experiments, etc.) designed for teachers and students of the physical sciences. Some of the resources are available only on CD-ROM, but most...
Exploratorium
Exploratorium: Science Snacks: Snacks From a Z
Here is a monumental list of ideas for science fair projects and experiments, organized alphabetically. Every one of them is a link to a full page, with pictures, of information about the idea. This site is a goldmine.
Colorado State University
Little Shop of Physics: The Amazing Physics of Everyday Objects
Try out these experiments you can do with items you might already have around the house: "Two Ball Bounce," "Cartesian Diver," "Straw Flute," "Bernoulli Ball," and others. Two experiments, "Imploding Pop Can" and "Balloon in a Bottle,"...
Fundación Cientec
Cientec: Fisica
Different step by step experiments in Physics. It explorer concepts such as adhesion, pressure, weight, movement, balance, energy and more.