If you're on Pinterest, chances are good you've seen this activity. But for the few who haven't, get ready for some seriously cheap science fun. We made a hovercraft! Supplies An old CD that you no longer need Glue gun and glue sticks thumbtack soda bottle screw top (you want one that's fairly deep) latex party balloon Assembly Poke several holes in the plastic bottle top with the thumbtack. Use a hot glue gun (Adults, please. No children. Those things are H-O-T) to apply a bead of glue to…