For asking this question, our junior science cadet, Alexander, wins a plastic whistle and a shiny sticker to put on his lunch pail!

Answer:
What occurs is explained by two of three laws of motion and the attraction/repulsion of atoms.

Knowledge was harnessed in this way by a manufacturer to amuse our primitive delight in gross phenomena.
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"Mankind is prone to seek an explanation of uncommon phenomena only, while the ordinary changes of nature, which are in themselves equally wonderful,are disregarded."

-- Almira Lincoln Phelps
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