What you’ll need
What you’ll need
- Two empty 0.5-liter plastic bottles with caps
- Water
- Strong, waterproof adhesive
- An awl
- A pocket knife
- A heavy book
Note: after the second step there’s a long wait.
How to do it
How to do it
1. Apply some glue to the top of both caps. Wait two to three minutes until the adhesive is dry to the touch.
2. Glue the two bottles cap together and place a heavy book on them. Now wait until the glue is completely dry. Depending on the glue this could take several hours. We recommend you leave it to dry overnight.
3. Ask an adult to make a hole through the cap with an awl.
4. Ask an adult to enlarge the hole using a pocket knife.
5. Fill one of the bottles to the top with water and attach the double cap. Make sure that you only grip the lower cap, so that the two caps don’t come apart.
6. Screw the second, empty bottle top down onto the second cap, holding the upper cap tightly as you do so.
7. Turn your construction upside down. Hold one bottle with each hand and rotate both bottles quickly in a circle around their own axis. Place your construction upright again.
8. The water flows from one bottle to the other. And what else happens?
Well spotted!
Well spotted!
When the bottles are motionless, the water doesn’t move. But after you rotate them, water flows from the upper bottle into the lower one and a water vortex is created.
What's the secret?
What's the secret?
The water doesn’t flow by itself from the upper bottle into the lower one. The surface tension of the water, in the small hole between the upper bottle and the air-filled bottle below, prevents it from doing so. When you rotate the bottles, the water in the bottle is set in motion – and it moves up the sides of the bottle. A channel forms in the center of the bottle through which air from the lower bottle passes upwards. The water in the upper bottle then flows in a downward spiral.
Water vortices – also called whirlpools – can also be spotted in everyday life, for example, when you pull the plug in the bath or stir a drink with a spoon. In nature, whirlpools can arise in narrow water straits due to the tides, or in rapids or waterfalls.
A tornado is also a type of vortex whereby powerful winds create a column of air that reaches from a cloud right down to the ground. Air-borne water droplets make the swirling winds of a tornado visible.
