Feeling the springiness of air

Class practical of air

Observing that air springs back when the pressure on it is released.

Apparatus and Materials

For each student group

• Plastic syringe
• Bicycle pump

Health & Safety and Technical Notes

Read our standard health & safety guidance

Procedure

1. Close the outlet of the syringe with a finger, and compress the air in the syringe. Notice its springiness as the force on it is increased or decreased.
2. Repeat with a bicycle pump.

Teaching Notes

• Take care: syringes can easily be filled with water! Whilst this will demonstrate that liquids are less compressible than gases and any air bubble remaining will shrink in size it might not be what the unwary teacher had in mind!
• Gases are squashy. Compressing a plastic syringe full of air allows you to feel its springiness as the piston bounces back as soon as the force is released.
• Questions to ask:
• How could you tell whether it is the air that makes it difficult to press the piston down, (the air that they can feel pressing back) or the piston rubbing the side of the barrel?
• What makes the air press on things?
• Gases can exert a considerable pressure on anything that holds them. How do they exert that pressure? What is pressure?
• Simple pressure-related activities:
• Shut your mouth and puff out your cheeks and feel your cheeks with your fingers.
• Feel the lightly compressed air in your chest driving out through your mouth and nose when you breathe out.
• Hear carbon dioxide bursting out from a bottle of lemonade.
• Feel gas escaping from a cylinder and listen to it.

The experiment was safety-checked in July 2007