How do police speed guns work?

Question

I'm just asking because i don't understand how a gun can see how fast a car is travelling.

Answer 1

Their radar guns send out high frequency radio waves, and examine the frequency of the signals that bounce back.  If a car is moving toward the radar gun, the arriving frequency is slightly higher than the outgoing frequency.  The radar gun displays the difference in frequency as miles per hour.  Google "doppler effect" to learn more.

If the police car is moving too, the radar gun factors its speed into the result.  The most sophisticated police radar I have seen can see backward, forward, and to each side.  It can even tell the speeds of teach of two approaching cars.  The equipment is so powerful that by the time most radar detectors see the signal the policeman already knows how fast you were going.

Answer 2

Doppler effect.

Answer 3

Nowaday,police is no more using radar gun because radar detector is existed in the market. Now they use lazer gun to measure the speed.

By measure the time difference between two reflect lazer beams,that giving the car travel speed.