Tornado In A    Bottle

A mini-twister.

 

 

 

Category - Force & Motion

Key Idea - Rotation

 

Purpose - The creation of a vortex in a bottle demonstrates angular momentum, surface tension, centripetal force and fluid displacement.  

 

A vortex in progress. 
Nature -  Demonstration with student assistance 
Materials -  two 2 litre plastic soft drink containers, a Tornado Tube™ bottle connector OR two bottle lids, some super glue, some electrical tape  and a drill. 
Method - 
  1. Fill one of the bottles with water (add some food colour and glitter if you wish)
  2. Connect both bottle together with the connector (see the Notes below to do this without the Tornado Tube™)
  3. Turn the bottles over and observe the movement of water from one to the other.
  4. Try again, but this time give the top bottle a few spirals as you set it down.  Note what happens this time.
Safety - Nil
Explanation - The first time you turn the bottles over the surface tension of the water tries to hold the water back, but the weight is such that a blob of water breaks through into the second bottle.  This happens several times, building up pressure in the bottom bottle until air is forced up into the top bottle.  And so on, until the top bottle is empty.

The second time the water started moving in a spiral and formed a vortex into the bottom bottle.  Gravity is pulling the spinning water down through the hole into the bottom bottle.  The angular momentum of the spinning water forces the water at the centre of the vortex to be spinning faster than the water on the edges.

The air in the bottom bottle is able to move out of the way of the incoming water buy moving through the centre of the vortex without disrupting the flow.  This, combined with the forces of water pressure and gravity force create the centripetal force that acts on the water. This can be seen by looking at the relative steepness of the vortex at the fast moving bottom compared with the slower moving top.  The higher the speed, the steeper the curve needed to allow the motion.
Notes -

To make your own tornado connector simply glue two bottle tops together, flat sides touching.  Once dry drill a hole through the centre of both lids with a 9 mm drill bit.  Screw in two bottles (one with water) and reinforce the join with some electrical tape.

Natural vortices include tornadoes, whirlpools and cyclones.