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.