Paper towel magic: Materials   Introduction This is a demonstration to help pupils understand, as part of an introduction to gases, that there is air occupying all the 'empty' spaces around them and that it has volume.

 

Lesson organisation
This is a short introductory activity. Depending on the prior experiences of the pupils it can be demonstrated as a 'magic trick' or presented as a 'challenge activity' with the 'trick' as the solution. You may also wish to give pupils the opportunity to try the activity for themselves afterwards.

Equipment and materials
• Clear plastic cup(s)

• Paper towels (or similar)

• Transparent bowl or tank of water, deeper than the cup

Technical notes and safety
Make sure the paper towel is pushed securely into the bottom of the cup and the cup is vertical as it is lowered into and lifted out of the water.

Procedure
a Show the tank, cups and paper towels to the pupils. Challenge the pupils to put a scrunched up paper towel into the water and bring it out dry. Let them demonstrate some of their ideas.

b If anyone is successful proceed with the discussion. Otherwise, scrunch a paper towel into the bottom of a dry cup. Invert the cup and lower it into the water until it is completely submerged. Lift it out and ask pupils to check that the towel is completely dry.

c Ask the pupils to talk with a partner and then discuss as a class how the 'magic trick' was done. Repeat the demonstration as necessary during the discussion to support further observation and explaining.

 

Click here to see a full list of Health and Safety procedures

 

Teaching notes
Some pupils will realise quite quickly that the air in the cup is stopping the water from reaching the towel. Others will need to see the cup being tilted, releasing bubbles of air, and watch the water rise to replace the air inside the cup before they can explain how the 'magic trick' works. A small amount of water rising in the cup before any air has been released demonstrates that air can be compressed.

Possible questions:
What is in the cup?
Is anything else in the cup?
What can you see when the cup is underwater?
Can you see any water in the cup?
What is stopping the water going into the cup?
How can I show there is air in the cup?
or What will happen if I tilt the cup?
What has happened to the towel now?

 

Click here to download this activity as a Microsoft Word document