How do mobile phones vibrate? They seem too small to have a spring inside!

The watched phone never rings - Day 329 of Project 365 by Matthew, on FlickrMobile phones are made to vibrate by a very small electric motor with an eccentrically mounted (off-centre) weight on the shaft (click here to see one). When the motor spins, this unbalanced weight makes the phone vibrate in exactly the same way that a solitary soggy duvet in a washing machine makes it shake, rattle and roll all over the kitchen.

The motors that are used in mobile phones really are very tiny: some of them aren’t much bigger than 4 mm across and maybe 10 mm long, with a shaft well under 1 mm in diameter. It wasn’t very long ago that these titchy motors were regarded as a mechanical marvel with a price tag to suit. Now we can make then by the million, and cheaply enough to use them in things like throw-away vibrating toothbrushes that sell for a fiver.

There are a variety of videos on YouTube, showing what these motors look like when you take them out of their phone or vibrating toothbrush.

Here’s a demo of a ringing mobile phone with the motor exposed:

Answer by Richard Ellam

Image source: Matthew, on Flickr

Article by Richard Ellam

August 18, 2014

Richard Ellam is a freelance science communicator, writer and historian specialising in engineering and physics. He designs and makes interactive exhibits and show props in a warm, well equipped workshop in the West of England, and also presents science shows all over the country. (see for more!)

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One thought on “How do mobile phones vibrate? They seem too small to have a spring inside!”

  1. Mobile phones are, in fact, made to vibrate by being connected, via a subspace wormhole, to a beehive or ant colony; it is the buzzing of wings or the stamping of tiny feet that makes your phone vibrate. Ain’t science grand.

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