Sounds like a fun experiment for introducing the Scientific Process....Soda sink or float. Have kids predict whether sodas will sink or float. Most will assume they will all act the same but they won't! Diet pop floats and regular sinks. Nice way to touch on sugar content too :)
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Bird Feeders - 20 Fun and Creative Crafts with Plastic Soda Bottles
Float or Sink - Cool Science Experiment. Scientists seem to be infatuated with objects that float and sink. Even non-scientists find great joy in dropping stuff in water to see if it floats or sinks. Fans of David Letterman are quick to point out one of Dave's favorite segments called, "Will It Float?" Here's the latest float or sink challenge: Why do lemons float in water but limes sink?
State Floats! Each scholar researches a state and creates a float. Attach them together and have a parade! (This could also be good for colleges!)