What you'll need:
Clear water bottle (with all paper removed), sticky note, marker, water
What you do:
On the sticky note, draw two arrows, pointing in opposite directions. Make sure you use a dark color marker and that your arrows are big and clear. Stick this onto a wall. Fill the clear water bottle with water, all the way to the top, and screw the cap back on. Gradually move the water-filled bottle in front of the sticky note. As the bottle moves in front of the sticky note, something amazing happens with the arrows! They appear to change direction!