• Question: How does a speedometer work?

    Asked by anon-267489 to Louisa, Katherine, Iain, Eleanor, David, Bradley, Adrien on 26 Nov 2020.
    • Photo: Iain Tullis

      Iain Tullis answered on 26 Nov 2020:

      An old school, mechanical one is a iron plate on a pivot (attached to the needle) and a spring and dragged by a rotating magnet connected to the wheels

      The modern method is to count the number of pulses from a toothed wheel over a period of time. You can calculate speed from that (knowing wheel diameter etc) . This is the modern method as there is a toothed wheel to measure the speed of each of the 4 wheels and this is used for the ABS brakes.

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