Demonstrating how simple hovercrafts work
CD disks, balloons, drink tops (Fruit Shoot type), hot glue gun
Glue the drink top to centre of the CD. Blow the balloon up and whilst one person holds it firmly so no air escapes, another person puts the balloon opening on to the closed bottle top. Place the CD on a flat surface (we found a table worked better than the floor), hold the bottle top firmly (otherwise it may separate from the CD), open the valve and watch the CD hover slightly above the surface.
This activity doesn't complete any badge requirements