Dancing raisins

Activity overview

Run the activity

1. You’re going to watch a short video. The aim isn't to find right answers, it's to explore ideas and find out what they know.

• Do they know what might happen based on the image?

2. After you've watched the video, lead a discussion with your class:

• What does the class think will happen when the raisins go into the bottle?
• Did they expect the raisins to behave in the way they did?
• Can they see the bubbles attached to the raisins? Why do they think these form?
• Why do the raisins travel up and down in the bottle?

3. Ask the class to describe what they saw using only one word.

Background science

This is a video of a handful of raisins being dropped into a bottle of fizzy soda water.

Gases do not have a fixed shape or volume. They spread out and change their shape and volume to fill whatever container they are in. Unlike liquids and solids, gases can be squashed. The carbon dioxide (CO₂) gas is compressed inside the bottle of soda water so that it dissolves in the liquid. When the lid is unscrewed the pressure is released and bubbles of gas start to form in the liquid. 

As the raisins are added to the liquid containing gas, they initially sink, because they’re denser than the liquid they've been dropped into, but as they travel through the liquid the gas bubbles forming in the soda water begin to attach themselves to the rough surface of the raisins. Look closely, you can see this happening in the video! These bubbles give the raisins buoyancy, so they rise to the top of the bottle. When they reach the surface the bubbles pop as the gas escapes out of the bottle and the raisins sink back down, for the process to start again.

When the lid of the bottle is screwed tightly there is a limit to the amount of CO₂ that can escape into the space above the liquid, so that you end up with equilibrium, and no more movement until the lid is unscrewed again and the gas bubbles form again.

Watch out for... 

Some children may believe gas is not a material because most gases are invisible. The bubbles in the liquid indicate that a gas, (CO₂ in this case), has been added to the liquid. This does not need to be corrected during the session, but you can pick it up later.

Take it further

Activities

Why not try this experiment in class using other fizzy liquids such as sparkling water or lemonade? Or investigate what happens with different objects, like chocolate chips or edible silver balls?

Watch 

Watch this BBC film to find out if fizzy or flat lemonade weighs more. 

Linked Explorify activities- our recommendations: 

Other Explorify activities that look at gases include: Gas.