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This demonstration consists of a bell jar mounted on a platform. Inside the bell jar a sound source is hanging from a support, and connected to a switch mounted external to the bell jar. The bell jar also has a fitting to attach a vacuum pump and a pressure release valve.
Demonstrate that sound waves require a medium to travel.
You will still hear a little noise from the alarm due to vibrations being transmitted by the supports inside the jar and the limits of the vacuum pump.
Take care when handling this demo. The glass bell jar is probably only held to the platform by the stickiness of the vacuum grease and the gasket used to make a seal.
Demo room information