Doppler Effect concepts

[lamborghiniMD]

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Okay, so I thought I knew the basic concepts but apparent I don't.

I get that if two objects are traveling at the same speed in the same direction, there is no Doppler Effect.

But imagine this scenario where object A is stationary picks up a sound (let's say X Hz) from an object B moving at 200m/s. How would this sound (X Hz) compare to these scenarios:

a. If object A suddenly moves with a speed of 200m/s East while picking up signals from object B traveling 200m/s West? ( A ----> <----- B)

b) If object A moves with a speed of 200m/s and object B moves with a speed of 400 m/s in the same direction (A --> B--->)

Thanks!

 

[Sports Junky]

Okay, so I thought I knew the basic concepts but apparent I don't.

I get that if two objects are traveling at the same speed in the same direction, there is no Doppler Effect.

But imagine this scenario where object A is stationary picks up a sound (let's say X Hz) from an object B moving at 200m/s. How would this sound (X Hz) compare to these scenarios:

a. If object A suddenly moves with a speed of 200m/s East while picking up signals from object B traveling 200m/s West? ( A ----> <----- B)

b) If object A moves with a speed of 200m/s and object B moves with a speed of 400 m/s in the same direction (A --> B--->)

Thanks!

In your original example (Scenario 1) , it matters whether or not object B is moving towards/away from object A. Object A = observer (detected frequency); Object B = source (emitted frequency)

If object B is moving towards A, then the detected frequency would be larger than the emitted frequency.

If object B is moving away from A, then the detected frequency would be smaller than the emitted frequency.

Scenario a) The observed frequency would be even larger than Scenario 1. This is because the relative speed towards the observer is larger.

Scenario b) The observed frequency will equal Scenario 1 if in the original scenario object B was moving away from Object A at 200m/s.

Overall, it is the relative speed either towards or away from the observer that is of utmost importance.

If the source is approaching the observer, then observed frequency > emitted frequency.
If the source is moving away from the observer, then observed frequency < emitted frequency.