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Tornado Maker

In this activity, students create a model of a vortex using water instead of air.

A vortex is a swirling mass of fluid (a liquid or a gas). We see vortices in nature when we see phenomena like whirlwinds, tornadoes and whirlpools, but you can create your very own vortex using a simple set-up of two pop bottles and a washer.

Gravity pulls water from the top bottle down into the bottom bottle. When you swirl the water, it rotates as it falls down. The water spiraling down from the top bottle into the bottom one moves faster and faster as it falls.

The faster a fluid moves, the lower its internal pressure (this is called Bernoulli's Principle, named after the scientist who discovered it). So, as the water in the top bottle spirals inward and down, getting faster and faster, its pressure decreases.

Where the water pressure is lower (in the centre of the bottle) the air above the water pushes it out of the way, making a hole. The water pressure in the tank also increases with depth, so the hole gets smaller towards the bottom of the tank, resulting in the "tornado" shape.

Objectives

  • Create a model of a vortex.

Materials

  • Per Student:
    2 narrow-mouthed pop bottles
    glitter
    water
    food colouring
    1 washer (that fits flush, or as close as possible, to the mouth of the bottles)
    heavy duty duct tape (30 cm)
    electrical tape (50 cm)

Key Questions

  • Why does the vortex allow air to flow freely?
  • Would this experiment work without the washer?
  • How does the tornado in a bottle relate to a real tornado?
  • Where could you see vortices in your everyday life?

What To Do

  1. Fill one of the bottles 2/3 full of water. Add glitter and food colouring. This will make the water movement easier to see.
  2. Place the washer on the top of the bottle.
  3. Place the second (empty) bottle upside down above the first (filled bottle). Carefully line up the two mouths and tape them together using duct tape, taking care to create a water tight seal. Seal further with electrical tape.

Teacher Tip: The better and more water-tight the seal, the more successful the vortex will be. You may need to lend a hand at this stage.

  1. To use the “tornado maker,” turn it over so that the bottle with the water is on top. Swirl the top bottle in a circular motion and watch carefully to find the column of air form at the core of your water vortex.

Extensions

  • Compare the speed at which a spun bottle and a still bottle will empty, discuss the reasons for any differences.
  • Adding a coloured oil makes for a more dramatic coloured tornado. Note: water based food colouring does NOT coolur oil.