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Sound travels by molecules in the air knocking into one another. Bang goes the Theory presenter, Jem, silences an angle grinder by removing the air – recreating conditions in space in a vacuum in a bell jar.
An angle grinder is suspended inside a vacuum in a bell jar, mirroring the classic demonstration of an alarm clock in a bell jar. When the grinder is turned on, no noise can be heard. As air is allowed into the jar, noise can be heard. In addition, sparks can be seen as carbon dust ignites in the atmospheric oxygen.
Pupils view the clip and produce a labelled diagram of the experiment to explain the scientific principles involved. Clip 14 from the Bang Goes the Theory teachers pack. To download the pdf please go to bbc.co.uk/schools/teachers/bang/
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