Experiment to show sound cannot travel through a vacuum
This classic experiment is beautifully illustrated in this mini-vidclip:
A bell can be heard ringing within a bell jar.
The bell jar is connected to a vacuum pump and the air is slowly removed.
Once a vacuum (no air particles) has been achieved, the pump is turned off and air is allowed to slowly re-enter the bell jar.
To obtain a full vacuum is very difficult (and involves expensive equipment!). This experiment in a lab will probably achieve 95% vacuum - but that is enough to see the effect.
The following video is a really old one - but the type of bell used was useful as you could actually see that the clanger was still moving when the sound was no longer audible.