Air Rings

Push the handle to make bubbles float into the liquid. Can you make a vortex?

Explanation

You can form bubbles most readily when you give the handle a short, sharp push.

This creates a bubble of air, but also shoots a jet of high pressure liquid directly beneath the centre of your bubble.

The bubble becomes an air ring when this high pressure liquid punches a hole through its centre. As liquid rushes through the hole, a vortex forms around the ring-shaped bubble.

When the energy from the vortex is lost, your air ring will break up into smaller bubbles!

Extras for Experts

You may have seen images or videos of dolphins and beluga whales blowing similar rings of air. These rings are different because they don’t immediately float to the water’s surface. Instead, the dolphins can play with them, shooting them sideways or down through the water.

Dolphins create these rings by making vortices using their fins. They blow air into this vortex. The air is then spun into the shape of a ring.

You might have noticed that the bubbles have surfaces like mirrors. This is due to total internal reflection, where light hits the bubble’s water-air interface at an angle that causes it to bounce off the bubble’s surface. The light then reflects into our eyes, creating the impression that the bubble has a mirrored surface.

Things to Try

You may see tiny bubbles spinning around the rim of your air ring, showing how the vortex forms the air ring.
Notice the tiny bubbles that remain in the fluid for a long time. These float very slowly to the surface because they experience a lot of drag for their size.
Take a large, deep clear bowl and fill it with water. Place your slightly cupped hand into the water palm-down, so that you trap a little bit of air in your palm. Ask a friend to look at this bubble of air from below, through the sides of the bowl. The air bubble looks like mercury! This is because light is reflecting off the bubble due to total internal reflection.
Here’s another way to see total internal reflection at work. Start a stream of water flowing horizontally from a raised garden hose so that the stream falls down in a curve. Shine a torch along the stream and you will notice that the light bends to follow the stream of water. What it is doing is bouncing off the ‘edges’ of the water stream where the water meets the surrounding air.

Questions to Ask

Have you seen dolphins or whales blowing air rings underwater? How do you think they do this?

Try an Activity

Make your own antibubbles
You’ve probably made regular bubbles before, but have you ever made antibubbles?

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