Bell in a Vacuum

We look at how a vacuum affects how sound travels. An alarm is set off and placed under a bell jar. The air is removed from the jar to create a vacuum. We can still see the hammer of the alarm clock moving, but cannot hear the sound. This demonstrates that sound cannot travel through a vacuum. Physics - Waves - Learning Points. Sound waves need a medium to travel through. Sound waves are affected by the pressure of a gas. In space, astronauts need radio waves to be able to communicate. A Twig Experiment Film. Let students experience real experiments in lab conditions anywhere, from setup, method all the way through to analysis and real-world application.