To make a tornado in a bottle you will need:
two 2-liter bottles, their cups and water.
Remove the labels from the bottles.
***For this part adult supervision is required.***
Make a small holes in the cups of the bottles, and use a glue gun to glue them together, back to back, so they will become air tight.
Pour two thirds of water into one of the bottles,
and connect them with the double cup you made.
Flip over so the bottle with water is on the top, and swirl the bottles holding by the top bottle.
You will see a tornado funnel in a top bottle.
The air from the bottom bottle pushes up, while the water swirls around and pours down.
For a visual effect you can add some sparkles into the water.
Have fun observing the tornado effect.
You can experiment, by adding different things to water, or maybe adding food colouring or colour lamp oil. You can also see what happens when you change the size of the hole in the cups.