Mechanical Waves and Sound

Mechanical Waves and Sound

Introduction

As you watch the pendulum of a grandfather clock move back and forth to mark the passage of time, how do we know it is correct? What about the movement of a pendulum, or spring, allows us to determine time? Simple harmonic motion is the repeated motion of an object that obeys Hooke's Law. That is, it repeats its motion and the force on the particles is proportional to the displacement from equilibrium. In this module we will start with the oscillation of particles and objects then move on to the motion of waves. We will discuss sound in detail as an example of a mechanical wave.

Module Lessons Preview

In this module, we will study the following topics:

What is simple harmonic motion and how is it displayed in an oscillation spring or pendulum?
How does a mechanical wave behave in terms of its motion and the transfer of energy?
How do waves interfere with each other and how can we use the principle of superposition to determine the result of the interference?
How can sound demonstrate some of the properties of mechanical waves?

Key Terms

Amplitude: The distance from the resting position (equilibrium) to the maximum displacement.
Constructive Interference: The increase in amplitude for the medium due to two waves passing a given point with amplitudes in the same direction.
Destructive Interference: The decrease in amplitude for a medium due to two waves passing a given point with amplitudes in opposite directions.
Doppler Effect: The apparent change in frequency due to the motion of an observer and source relative to each other.
Frequency: The number of complete oscillations that occur per second, measured in Hertz.
Mechanical Wave: A wave disturbance that travels through a physical medium.
Medium: The substance that a mechanical wave disturbs.
Pendulum: A large mass on a nearly massless string that oscillates back and forth.
Period: The time required for one complete oscillation.
Simple Harmonic Motion: Periodic motion where the particles in oscillation obey Hooke's Law.
Spring: A coil that once set in motion will follow simple harmonic motion.
Superposition: Adding the amplitude of two waves to get the pattern for interference.
Wave: A disturbance of a medium that transfers energy but only allows oscillation of particles.
Wavelength: The distance from one point on a wave to the same point on the adjacent wave.

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