Activity: Tornado in a bottle

Nikita with her tornado bottles.

On SCOPE's water park science episode, you saw Nikita make a kind of tornado a bottle. Here’s how she did it. Watch the clip.

What you need

• Two plastic soft drink bottles
• A washer
• Electrical tape
• Food colouring
• Glitter

What to do

1. Fill one of the bottles about two-thirds full of water.
2. You can add food colouring for effect and a little glitter for sparkle!
3. Place the washer on the top of the bottle and then put the second bottle upside down on top of the washer.
4. Now you need to tape the two bottles firmly together with the washer in the middle. The idea is to make it water-tight, so use plenty of tape and push it into all the grooves..
5. Turn the tornado bottles upside down so the water-filled bottle is on the top and watch what happens.

What's happening?

When you invert the bottles, the water is trying to move into the bottom bottle, but it can’t while the bottom bottle is full of air. To make space for the water to go in, the air needs to be pushed out.

The only way for the air to go is up, but that path is being blocked by the water!

But what happens if we add a little centripetal force by rotating the bottle and getting the water swirling? A vortex, or whirling mass of water, forms!

The water’s inertia causes it to be hurled towards the walls of the bottle creating a space in the middle, which is the centre of the vortex.

The water at the narrow part of the vortex, near where the bottles join, is moving faster than the water at the top. At this narrow point, the water is closer to the centre and has a smaller distance to cover, so spins faster. It’s just like when an ice skater pulls her arms in to gain maximum speed during her spin. Not only does the water move faster but also more freely!

The vortex drains rapidly into the bottle below as the hole in the vortex allows the trapped air to escape.

When water gets swirling in a circular motion, centripetal force keeps things centred!