• Question: How does a laser speed gun work to measure a car's speed?

    Asked by hom001 to Mike, Pip, Tianfu, Tim, Tom on 29 Jun 2012.
    • Photo: Tim Stephens

      Tim Stephens answered on 29 Jun 2012:

      It works by sending two (or maybe more) laser pulses towards the car and measuring how long it takes for them to return to the speed gun. THe electronics inside the speed gun know the time between the pulses when they were sent, and they measure the time between them when they return. The faster the car is travelling, the closer together the reflected pulses are, and the speed gun can calculate the speed of the car.

    • Photo: Tom Lister

      Tom Lister answered on 29 Jun 2012:

      There are also Doppler ones, which measure the change in wavelength of the beam caused by hitting something moving.

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