Try this: Antibubbles

This week we will make anti-bubbles. An anti-bubble is like a bubble in reverse. It has water inside it, water outside it and a thin shell of air in between.

You will need

• A squeeze bottle with a nozzle, the type you use for squirting tomato sauce. Make sure that the bottle is clean.
• A jar
• A bowl
• A jug or other container that holds a larger volume than the jar and squeeze bottle combined.
• Water
• Detergent
• Food colouring (optional)

What to do

Preparation

1. Fill the jug with enough water to fill the jar and squeeze bottle.
2. Mix in some detergent. Use about twice as much as you would use to do the dishes.
3. Place the jar in the bowl.
4. Fill the jar until it is starting to overflow. If there are any bubbles on the top, gently blow them off.
5. Fill the squeeze bottle. You are now ready to make some antibubbles.

Making antibubbles

1. Tilt the bottle over so it is pointing downwards at about a 45 degree angle.
2. Hold the nozzle of the bottle a couple of centimetres from the surface of the water.
3. Give the bottle a quick squeeze. If you are lucky, you will find an antibubble forms in the jar and slowly rises to the surface.
4. Try giving the bottle gradually longer squeezes, you should find you can create larger anti-bubbles.
5. As you squeeze water into the jar, some of it will run over the edge into the bowl. When the bottle starts to run low, you can just lift up the jar, squeeze some of the air out of the bottle and suck the water from the bowl into the bottle.

Blowing antibubbles takes practise. You need to squeeze water into the jar at just the right speed, angle and height above the jar. If the antibubbles are only forming on the surface, try squeezing a bit harder. You may find it is easier to blow antibubbles if you add some more detergent to the water. Once you can make antibubbles, you could try adding some food colouring to the bottle, to show there is water inside the antibubble.

How to tell an antibubble from a normal bubble

• Bubbles and anti-bubbles both float towards the surface, but antibubbles float slowly.
• When antibubbles reach the surface, they sit under the surface of the water, not on top of it like normal bubbles.

What's happening?

An antibubble in water is the opposite of a normal bubble in the air.

• A normal bubble has air inside, air outside and a thin layer of water in between them.
• An antibubble has water inside, water outside and a thin layer of air between them.

When you squirt the water into the jar, a thin layer of air was caught between the water in the jar and the water squirting into it. When you squirt just right, this thin layer of air can be carried under the water and the surface of the water in the jar will close over it. This forms an antibubble.

Antibubbles are mostly water with a little bit of air. Although they will float, they are much heavier than a bubble of air, so they only move to the surface slowly. This extra weight is also why they float just under the surface instead of on it.

When I first saw an antibubble, I wondered why the water inside didn't just fall through the air and join with the water outside. It turns out to be because of the detergent. Detergent molecules have an electrical charge at one end, which makes them repel each other slightly. The detergent molecules inside and outside of the antibubble repel each other just enough to stop the water inside the antibubble touching the water outside.

There hasn't been much research done into the properties of antibubbles. How they form and burst is still not fully understood.