No, the sound frequency of a car does not change for people on both sides of the vehicle if it is moving at a constant velocity.
When a car is moving at a constant velocity, the sound it produces, such as the engine noise or the sound of the tires, remains unchanged in frequency. This is because the frequency of a sound wave is determined by the source of the sound, in this case, the car, and is not affected by the motion of the car itself.
However, there is a phenomenon called the Doppler effect that can cause a change in perceived frequency when there is relative motion between the source of the sound and the observer. The Doppler effect occurs when there is a relative motion between the source of the sound and the observer, resulting in a perceived shift in the frequency of the sound.
For example, if a car is moving towards an observer, the sound waves will be compressed, leading to a higher perceived frequency (higher pitch) compared to the actual frequency of the sound. Conversely, if the car is moving away from the observer, the sound waves will be stretched, resulting in a lower perceived frequency (lower pitch) compared to the actual frequency of the sound.
However, if the car is moving at a constant velocity and an observer is stationary or moving at the same velocity as the car, there will be no relative motion between the source of the sound and the observer, and therefore, no change in the perceived frequency of the sound for people on both sides of the vehicle.