how do road radars work?

Answer 1

Radar uses the doppler principle to determine speed. Doppler principle describes the way certain 'waves' change based on the distance and speed of moving objects. The best example of this is a train whistle as it moves toward you at speed. The sound changes as the approaches because you are hearing the sound waves being 'compressed' and then it changes again as the train passes because the waves are being 'stretched'.

A radar device emits a radio frequency wave which has a set interval between each wave. Each wave then travels down the road and hits a target (car) and returns back. As the target approaches or goes away the time interval of the returning waves are different from when they were emitted and a mathmatical calculation can be used to determine how fast the target is moving.

Laser guns work the same except that use pulsing laser beams instead of radar waves. Laser guns are more accurate and can be tightly targeted in order to pick on very specific targets from a group of targets.

Hope this answers the question!

Answer 2

The simple way to understand this is as follows. The stationary radar sends a wave at your moving vehicle. Your car reflects the wave and sends it back to the radar. This tels the radar where you are. It then sends another wave at your car and it calculates the difference between the two hits and translates this in to speed by calcuating the time to cover the distance from the second hit.