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The frequency of sound refers to how often the air pressure waves hit the listener's ear per second. It's measured in Hertz (Hz) and affects the pitch that we perceive. When discussing the Doppler effect, the concept of frequency becomes essential. The Doppler effect causes the observed frequency to change when either the source or the observer is moving relative to each other. The frequency emitted by the source remains constant, but how it is perceived depends on their relative velocities. For example, when a sound source approaches, the waves bunch up, leading to a higher frequency or pitch. Conversely, when the source moves away, the waves spread out, resulting in a lower frequency. Importantly, to calculate changes in observed frequency, we use the Doppler Effect equation, which considers both the speed of sound and the velocities of the source and listener. This addition or subtraction of velocities directly impacts the frequency heard by the observer.

The speed of sound is a fundamental constant for understanding how sound travels through air or any medium. For this exercise, the speed of sound in air is given as 340 m/s, which is a standard approximation at sea level and room temperature. The speed of sound plays a crucial role in the Doppler effect calculations. It represents the speed at which sound waves propagate through the medium. Variations in speed based on different media or conditions can alter how sound is perceived. Understanding this speed is important because it's the baseline value in the Doppler formula, against which the movements of listeners and sources are compared. In our problem, both the source and the observer's velocities are added or subtracted from this speed to determine the observed frequency. Thus, mastering this concept helps in grasping situations where sound frequency changes dynamically due to motion.

Wave motion is how sound waves travel through the air from the source to the listener. These waves are mechanical waves, which require a medium, such as air, to propagate. Sound waves are longitudinal waves, meaning the air particles move parallel to the direction of wave travel. This is different from transverse waves, where the motion is perpendicular. Each wave consists of compressions and rarefactions. Compressions are regions where particles are closer together, while rarefactions are regions where they are farther apart. In the context of the Doppler effect, wave motion is essential because it explains how changes in frequency occur. The closer the sound source gets to the observer, the shorter the distance between successive waves, increasing the frequency. Conversely, as the source moves away, this distance increases, lowering the frequency. Understanding wave motion helps us visualize problems involving sound and aids in applying mathematical equations efficiently to real-world problems like those involving the Doppler effect.