I've noticed that there are many threads here with people looking for science fair ideas, so now instead of starting a new thread, you can simply look here.

 

If you have any ideas for a science fair project, please post a reply with your idea. Lets try to make a big collection!

• Demonstrate (on a model scale) how you would blow up the school using minimal explosives that are easily produceable.
  
• Spin some fire poi to demonstrate how the eye isn't as fast as you'd think and will show you just lines of orange.
  
• Play whatever instrument you can play and say that your display has got something to do acoustics.
  
• Drink lots of tea and write about the various health benifits.
  

Something that I did today (as an alternative to doing anything constructive) was boiling water in a paper cup using a bunsen burner. Because there's no oxygen on the water-side of the cup, you don't get any combustion.

This is impressive ("everyone look at the magical unburnable cup!") and will make you popular with your teachers ("now I've boiled this water, have a cup of tea!").