# quick conceptual doppler question

#### SaintJude

##### Full Member
EK says that doppler effect can only occur with objects with a relative velocity. If two objects are moving at the same velocity, the perceived frequency = the real frequency.

Two objects are emitting sound waves in air. They are approaching each other at the same speed. Will they experience a doppler effect?

#### milski

##### 1K member
5+ Year Member
EK says that doppler effect can only occur with objects with a relative velocity. If two objects are moving at the same velocity, the perceived frequency = the real frequency.

Two objects are emitting sound waves in air. They are approaching each other at the same speed. Will they experience a doppler effect?

Yes. Approaching each other means that they have different velocities. Same speed in that case would mean same magnitude but opposite direction. The velocities will be s and -s. (as vectors, don't know how to draw the error on top here).

#### MedPR

##### Membership Revoked
Removed
EK says that doppler effect can only occur with objects with a relative velocity. If two objects are moving at the same velocity, the perceived frequency = the real frequency.

Two objects are emitting sound waves in air. They are approaching each other at the same speed. Will they experience a doppler effect?

Yes, and as milski already said, approaching objects may have the same speed, but cannot have the same velocity.

If two objects have the same velocity, the difference between their velocities is 0, so it's pretty much the same effect (no effect) as if they were both stationary.

#### umdnjmed

##### Full Member
10+ Year Member
5+ Year Member
I also have a quick conceptual question about doppler effect so I figured i'd just revive this thread. If the source and observer are moving towards each other, observed frequency increases. What if both are moving in the same direction and the velocity of the source is greater than that of the observer; since the source eventually catches up with the observer, would the observed frequency be higher in this case?

#### pm1

##### Full Member
I also have a quick conceptual question about doppler effect so I figured i'd just revive this thread. If the source and observer are moving towards each other, observed frequency increases. What if both are moving in the same direction and the velocity of the source is greater than that of the observer; since the source eventually catches up with the observer, would the observed frequency be higher in this case?

It would be higher up until the point where it reaches the observer. Once it reaches the observer while they are moving parallel to each other (together) the observed frequency will equal the source frequency. If the source continues to go faster than the observer the observed frequency will start to decrease. Because it is as if the source is moving away from the observer. I hope I didn't make it more confusing.

#### umdnjmed

##### Full Member
10+ Year Member
5+ Year Member
It would be higher up until the point where it reaches the observer. Once it reaches the observer while they are moving parallel to each other (together) the observed frequency will equal the source frequency. If the source continues to go faster than the observer the observed frequency will start to decrease. Because it is as if the source is moving away from the observer. I hope I didn't make it more confusing.

Thank you and no you didn't make it one bit confusing, you were very clear!

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