- Home
- Search
- Settings
- Top Contributors
- Help Center
How is radar used to determine the speed of moving objects?
Answer:
The "radar gun" is not the same as position-finding radar. Using microwaves (or a pulsed laser), it determines the speed of an object by measuring the change in the frequency of the waves when they are reflected back toward the gun.
In this application it is useful to think of light as a series of waves. Radar then is radio frequency waves sent out from the radar gun to the vehicle under consideration. These waves travel at a set speed that is constant, nothing can change how fast they go, but the distance the waves are from each other can be varied. This spacing of the radio waves is referred to as the frequency.
The closer the waves are to each other, then more of them can travel past a certain point in a given second. The farther apart the waves are, the number passing a certain point in any given second will be lower. Frequency then is a measurement of number of waves per second passing a certain point. Usually we don't consider unit-less values in such measurements so frequency is just considered to be (/second), (per second), or Hertz.
When a radio wave strikes a car it is reflected back the way it came, back to the radar gun where there is a coil that can detect them. If the radar gun were fired at a stationary wall the frequency of the waves coming back would be exactly the same as the frequency of the waves going out, and the instrumentation of the gun would interpret this as a stationary object.
If the wall was moving towards the gun however, then, in the time between the successive radio waves striking the wall, the wall moved a little bit closer to the gun. This makes the second radio wave get reflected sooner and the second wave travels back to the gun closer to the first wave then when the two of them left the gun. This is an increase in frequency. The radio waves are still traveling at the same speed (the speed is always constant, can't vary) but they are closer to each other, more concentrated.
The instrumentation in the radar gun detects this change in frequency and uses it to calculate the speed of the approaching wall. It works the same way to determine the speed of a car.
In this application it is useful to think of light as a series of waves. Radar then is radio frequency waves sent out from the radar gun to the vehicle under consideration. These waves travel at a set speed that is constant, nothing can change how fast they go, but the distance the waves are from each other can be varied. This spacing of the radio waves is referred to as the frequency.
The closer the waves are to each other, then more of them can travel past a certain point in a given second. The farther apart the waves are, the number passing a certain point in any given second will be lower. Frequency then is a measurement of number of waves per second passing a certain point. Usually we don't consider unit-less values in such measurements so frequency is just considered to be (/second), (per second), or Hertz.
When a radio wave strikes a car it is reflected back the way it came, back to the radar gun where there is a coil that can detect them. If the radar gun were fired at a stationary wall the frequency of the waves coming back would be exactly the same as the frequency of the waves going out, and the instrumentation of the gun would interpret this as a stationary object.
If the wall was moving towards the gun however, then, in the time between the successive radio waves striking the wall, the wall moved a little bit closer to the gun. This makes the second radio wave get reflected sooner and the second wave travels back to the gun closer to the first wave then when the two of them left the gun. This is an increase in frequency. The radio waves are still traveling at the same speed (the speed is always constant, can't vary) but they are closer to each other, more concentrated.
The instrumentation in the radar gun detects this change in frequency and uses it to calculate the speed of the approaching wall. It works the same way to determine the speed of a car.
First answer by Wolfgang schwartzschild.
Last edit by Wolfgang schwartzschild.
Contributor trust: 533
[recommend contributor
recommended].
Question popularity:
1
[recommend question].
