Problem 41 - Pearson Physics

Question

The sound you hear from a moving horn has a greater frequency than the sound produced by the horn. Is the horn moving toward you or away from you? Explain.

Step-by-Step Solution

Answer

The horn is moving toward you.

Step 1: Understand the Doppler Effect

The Doppler Effect describes the change in frequency of a wave in relation to an observer moving relative to the wave source. When the source approaches the observer, the frequency increases, leading to a higher pitch. Conversely, as the source moves away, the frequency decreases.

Step 2: Identify the Given Information

You are given that the frequency of the sound you hear is greater than the frequency of the sound produced by the horn. This means the sound waves have a higher frequency as they reach you.

Step 3: Determine the Direction of Motion Using Frequency Information

According to the Doppler Effect, an increase in the observed frequency (higher pitch) occurs when the sound source is moving towards the observer. Therefore, if you hear a higher frequency, the horn must be moving toward you.

Key Concepts

Frequency Change

In the context of sound waves, frequency change is an important concept that helps us understand how the pitch of sounds we hear can vary. Frequency refers to the number of waves that pass a point in one second, measured in Hertz (Hz). When we talk about a frequency change, we're describing a situation where this number increases or decreases based on the motion of the source relative to the observer. This is one of the core aspects of the Doppler Effect.

• When the source of the sound is moving towards you, the waves are compressed, leading to an increase in frequency. This makes the sound higher in pitch.
• Conversely, if the source moves away, the waves are stretched out, decreasing the frequency and resulting in a lower pitch.

These changes might not always be obvious, especially if the speed of the source is relatively slow, but they become very noticeable with fast-moving objects.

Wave Source Motion

Wave source motion describes how the movement of a sound source affects the sound waves it produces. This concept is key to understanding the Doppler Effect, which explains why we experience frequency changes with moving sound sources. The speed and direction of the wave source's motion relative to a stationary observer significantly influence the frequency heard.

• If the source is moving towards the observer, waves are bunched closer together, increasing their frequency.
• If the source is moving away, waves spread out, leading to a lower frequency being detected.

Understanding wave source motion is essential in scenarios like determining the movement of vehicles from the pitch of their horns or sirens. This knowledge can be crucial not only for physics but also for practical applications such as radar tracking or speed detection.

Sound Waves

Sound waves are mechanical waves that travel through mediums like air, water, or solids. They are characterized by their frequency, wavelength, amplitude, and speed. For the Doppler Effect to be observed, it's important to recognize how sound waves behave.

• The frequency of sound waves determines how high-pitched or low-pitched a sound is.
• Wavelength is the distance between successive crests of a wave.
• The amplitude of a sound wave affects how loud it is.

When a sound source moves, the properties of these sound waves change in relation to the observer, which is the principle behind the Doppler Effect. Remember that sound waves require a medium to travel through, which is why we can't hear them in a vacuum. Observing how sound waves interact in our environment can teach us a lot about physics and help us understand everyday phenomena.