An investigation into how sound travels through the air. An alarm clock is placed in a special jar. As the air inside the jar is pumped out, the alarm bell becomes quieter and quieter. When the air has been completely emptied from the jar, the bell can't be heard at all, although it is still ringing. The air is allowed back into the jar and the bell can then be heard again.

This clip is from:
Science Clips, Changing Sounds
First broadcast:
12 October 2007

When investigating which materials sound can travel through, this clip could be used before or after pupils conduct their own experiments to test which are the best sound insulators. Children could begin by exploring which classrooms in the school have the most effective sound insulation and could also use this clip to inspire designs for sound insulation music rooms.